Add the ability to send local images to external viewer
Add the ability to send local images to external viewer

This is needed for the implementation of #3438.

auricgoldfinger/cgeo,cgeo/cgeo,samueltardieu/cgeo,madankb/cgeo,ThibaultR/cgeo,ThibaultR/cgeo,samueltardieu/cgeo,kumy/cgeo,brok85/cgeo,superspindel/cgeo,KublaikhanGeek/cgeo,tobiasge/cgeo,ThibaultR/cgeo,pstorch/cgeo,brok85/cgeo,lewurm/cgeo,kumy/cgeo,samueltardieu/cgeo,rsudev/c-geo-opensource,superspindel/cgeo,rsudev/c-geo-opensource,SammysHP/cgeo,KublaikhanGeek/cgeo,Bananeweizen/cgeo,madankb/cgeo,auricgoldfinger/cgeo,Huertix/cgeo,yummy222/cgeo,mucek4/cgeo,madankb/cgeo,vishwakulkarni/cgeo,auricgoldfinger/cgeo,Bananeweizen/cgeo,matej116/cgeo,cgeo/cgeo,marco-dev/c-geo-opensource,mucek4/cgeo,pstorch/cgeo,S-Bartfast/cgeo,yummy222/cgeo,SammysHP/cgeo,mucek4/cgeo,matej116/cgeo,yummy222/cgeo,schwabe/cgeo,rsudev/c-geo-opensource,lewurm/cgeo,schwabe/cgeo,marco-dev/c-geo-opensource,pstorch/cgeo,tobiasge/cgeo,matej116/cgeo,Bananeweizen/cgeo,xiaoyanit/cgeo,xiaoyanit/cgeo,SammysHP/cgeo,schwabe/cgeo,kumy/cgeo,schwabe/cgeo,xiaoyanit/cgeo,cgeo/cgeo,KublaikhanGeek/cgeo,Huertix/cgeo,vishwakulkarni/cgeo,tobiasge/cgeo,cgeo/cgeo,vishwakulkarni/cgeo,S-Bartfast/cgeo,lewurm/cgeo,marco-dev/c-geo-opensource,superspindel/cgeo,Huertix/cgeo,S-Bartfast/cgeo,brok85/cgeo