refactoring: visit cache activity cleanup
refactoring: visit cache activity cleanup

* use alert dialogs instead of context menus
* simplify update logic
cgeo/cgeo,mucek4/cgeo,cgeo/cgeo,madankb/cgeo,lewurm/cgeo,tobiasge/cgeo,schwabe/cgeo,Huertix/cgeo,madankb/cgeo,pstorch/cgeo,lewurm/cgeo,superspindel/cgeo,rsudev/c-geo-opensource,schwabe/cgeo,brok85/cgeo,marco-dev/c-geo-opensource,marco-dev/c-geo-opensource,KublaikhanGeek/cgeo,vishwakulkarni/cgeo,SammysHP/cgeo,yummy222/cgeo,matej116/cgeo,kumy/cgeo,brok85/cgeo,xiaoyanit/cgeo,kumy/cgeo,tobiasge/cgeo,ThibaultR/cgeo,S-Bartfast/cgeo,samueltardieu/cgeo,matej116/cgeo,brok85/cgeo,samueltardieu/cgeo,S-Bartfast/cgeo,ThibaultR/cgeo,schwabe/cgeo,pstorch/cgeo,Bananeweizen/cgeo,Huertix/cgeo,xiaoyanit/cgeo,mucek4/cgeo,samueltardieu/cgeo,matej116/cgeo,pstorch/cgeo,SammysHP/cgeo,cgeo/cgeo,cgeo/cgeo,marco-dev/c-geo-opensource,SammysHP/cgeo,vishwakulkarni/cgeo,yummy222/cgeo,tobiasge/cgeo,KublaikhanGeek/cgeo,rsudev/c-geo-opensource,rsudev/c-geo-opensource,auricgoldfinger/cgeo,superspindel/cgeo,ThibaultR/cgeo,S-Bartfast/cgeo,yummy222/cgeo,auricgoldfinger/cgeo,schwabe/cgeo,Bananeweizen/cgeo,madankb/cgeo,Huertix/cgeo,KublaikhanGeek/cgeo,vishwakulkarni/cgeo,auricgoldfinger/cgeo,xiaoyanit/cgeo,mucek4/cgeo,Bananeweizen/cgeo,superspindel/cgeo,lewurm/cgeo,kumy/cgeo