Add optional class to FieldLabel.
Add optional class to FieldLabel.

Andrews9008/blockly,markocelan/blockly-minecraft,google/blockly,touqir14/blockly,Gamefroot/Gamefroot-Blockly,google/blockly,carlosperate/blockly,nickmain/blockly,jano42/blockly,aseba-community/blockly,drigz/blockly,CocoMake7/CocoBlockly,eclecticdave/blockly,wakashige/blockly,jstnhuang/blockly,gudtago/blockly,twodee/blockly,toebes-extreme/blockly,picklesrus/blockly,jstnhuang/blockly,CocoMake7/CocoBlockly,sclements/scratch-blocks,cmillani/blockly,MaryS94/blockly,aseba-community/blockly,drigz/blockly,zerar/blockly,rachel-fenichel/blockly,hkoi/blockly,rachel-fenichel/blockly,dhalupa/blockly,trodi/blockly,3agv2004/Programming,sonwh98/blockly,carlosperate/blockly,twodee/blockly,touqir14/blockly,RealTimeWeb/blockly,marianoguerra/blockly,gupta137/blockly,lzairdking/blockly,trinketapp/blockly,google/blockly-devtools,carloslfu/blockly,ralic/blockly,mark-friedman/blockly,carloslfu/blockly,gengshenghong/scratch-blocks,carlosperate/ardublockly,sonwh98/blockly,andersschuller/blockly,OpenRoberta/blockly,groklearning/blockly,jano42/blockly,Tinkerforge/tvpl-blockly,jano42/blockly,TechplexEngineer/blockly,michalkilawok/blockly,edbutler/blockly,SheldonPacotti/blockly-enhancements,Tinkerforge/tvpl-blockly,UIKit0/blockly,google/blockly,HALtheWise/blockly,cmillani/blockly,OpenRoberta/blockly,nickmain/blockly,carloslfu/blockly,wakashige/blockly,stefan-j/blockly,griffpatch/scratch-blocks,jano42/blockly,griffpatch/scratch-blocks,TechplexEngineer/blockly,in1004kyu/tokitool,hkoi/blockly,markocelan/blockly-minecraft,rasata/blockly,zerar/blockly,ChinJY/blockly,dhalupa/blockly,griffpatch/scratch-blocks,vinay5jan/blocklyExtended,sonwh98/blockly,carlosperate/blockly,joshlory/blockly,zerar/blockly,eclecticdave/blockly,marianoguerra/blockly,sclements/scratch-blocks,ralic/blockly,google/blockly,ocadotechnology/blockly,trinketapp/blockly,InspectorWidget/blockly,aninternetof/blockly,toebes-extreme/blockly,LLK/scratch-blocks,nickmain/blockly,ChinJY/blockly,toebes-extreme/blockly,sclements/scratch-blocks,trodi/blockly,cmillani/blockly,trinketapp/blockly,altereagle/blockly,eclecticdave/blockly,LLK/scratch-blocks,aninternetof/blockly,gengshenghong/scratch-blocks,rasata/blockly,stefan-j/blockly,andersschuller/blockly,Immortalin/blockly,twodee/blockly,LLK/scratch-blocks,vinay5jan/blocklyExtended,lzairdking/blockly,hybrideagle/blockly,InspectorWidget/blockly,google/blockly,nickmain/blockly,mark-friedman/blockly,groklearning/blockly,Gamefroot/Gamefroot-Blockly,groklearning/blockly,aseba-community/blockly,dhalupa/blockly,nickmain/blockly,google/blockly-devtools,stefan-j/blockly,SheldonPacotti/blockly-enhancements,carlosperate/blockly,aravart/speech-blocks,andersschuller/blockly,Immortalin/blockly,google/blockly,gupta137/blockly,griffpatch/scratch-blocks,picklesrus/blockly,Tinkerforge/tvpl-blockly,trodi/blockly,twodee/blockly,picklesrus/blockly,markocelan/blockly-minecraft,rachel-fenichel/blockly,google/blockly,gengshenghong/scratch-blocks,marianoguerra/blockly,michalkilawok/blockly,stefan-j/blockly,rasata/blockly,hybrideagle/blockly,edbutler/blockly,LLK/scratch-blocks,daarond/blockly,markocelan/blockly-minecraft,thr0w/blockly,in1004kyu/tokitool,UIKit0/blockly,UIKit0/blockly,sclements/scratch-blocks,griffpatch/scratch-blocks,vinay5jan/blocklyExtended,gudtago/blockly,Andrews9008/blockly,OpenRoberta/blockly,HALtheWise/blockly,rachel-fenichel/blockly,Andrews9008/blockly,jisqyv/blockly,jstnhuang/blockly,mark-friedman/blockly,RealTimeWeb/blockly,twodee/blockly,michalkilawok/blockly,aninternetof/blockly,carlosperate/ardublockly,twodee/blockly,hkoi/blockly,mark-friedman/blockly,gengshenghong/scratch-blocks,ocadotechnology/blockly,nickmain/blockly,ralic/blockly,touqir14/blockly,rachel-fenichel/blockly,mark-friedman/blockly,RealTimeWeb/blockly,altereagle/blockly,joshlory/blockly,trinketapp/blockly,wakashige/blockly,gudtago/blockly,edbutler/blockly,InspectorWidget/blockly,shabesoglu/blockly,shabesoglu/blockly,groklearning/blockly,hybrideagle/blockly,SheldonPacotti/blockly-enhancements,altereagle/blockly,rachel-fenichel/blockly,Immortalin/blockly,lzairdking/blockly,shabesoglu/blockly,Gamefroot/Gamefroot-Blockly,jstnhuang/blockly,in1004kyu/tokitool,MaryS94/blockly,3agv2004/Programming,jisqyv/blockly,LLK/scratch-blocks,jisqyv/blockly,drigz/blockly,Gamefroot/Gamefroot-Blockly,MaryS94/blockly,gupta137/blockly,thr0w/blockly,daarond/blockly,OpenRoberta/blockly,thr0w/blockly,mark-friedman/blockly,HALtheWise/blockly,trodi/blockly,daarond/blockly,ocadotechnology/blockly,sclements/scratch-blocks,joshlory/blockly,carlosperate/ardublockly,3agv2004/Programming,lzairdking/blockly,aravart/speech-blocks,gengshenghong/scratch-blocks,CocoMake7/CocoBlockly,ChinJY/blockly,rachel-fenichel/blockly