collection of current issues with GraphicFeature

• events info is becoming a bit of a mess and needs more consistency with information returned by events, Cleanup GraphicFeatures events pick_info  #174
• support selections of multiple indices for collections (like selecting multiple contours or temporal traces with Ctrl + click for example). This would also involve changes to Interaction
• GraphicCollection feature data is not accessible #123
• refactor ImageCmapFeature #132
• Implement fancy indexing for GraphicFeatures #101
• graphic features, part 2 #85
• allow passing unique integers for color labels, useful for sklearn classifier outputs: