Added comment and renamed variable
Added comment and renamed variable

* Renamed $clipboardUpload to $previewUpload
* Added comment to non-obvious $uploadCallback

M-Zuber/JabbR,mzdv/JabbR,fuzeman/vox,yadyn/JabbR,SonOfSam/JabbR,e10/JabbR,timgranstrom/JabbR,lukehoban/JabbR,JabbR/JabbR,JabbR/JabbR,18098924759/JabbR,fuzeman/vox,borisyankov/JabbR,lukehoban/JabbR,fuzeman/vox,borisyankov/JabbR,timgranstrom/JabbR,LookLikeAPro/JabbR,mzdv/JabbR,CrankyTRex/JabbRMirror,CrankyTRex/JabbRMirror,LookLikeAPro/JabbR,CrankyTRex/JabbRMirror,yadyn/JabbR,LookLikeAPro/JabbR,e10/JabbR,M-Zuber/JabbR,ajayanandgit/JabbR,18098924759/JabbR,borisyankov/JabbR,lukehoban/JabbR,ajayanandgit/JabbR,SonOfSam/JabbR,yadyn/JabbR