As part of #136: CollectionPage was iterating its parent's list to ensure the same photo was not added twice to  its view.  Smart!  CollectionPage now maintains a HashMap of LibraryPhoto -> Thumbnail.
As part of #136: CollectionPage was iterating its parent's list to ensure the same photo was not added twice to 
its view.  Smart!  CollectionPage now maintains a HashMap of LibraryPhoto -> Thumbnail.


damianmoore/shotwell,Sanva/shotwell-gsoc,h4ck3rm1k3/shotwell,damianmoore/shotwell,h4ck3rm1k3/shotwell,jof/shotwell,jimbonator/shotwell,polymeris/shotwell,abrauchli/shotwell,ritchiewilson/shotwell,Sanva/shotwell-gsoc,abrauchli/shotwell,jimbonator/shotwell,jof/shotwell,polymeris/shotwell,ritchiewilson/shotwell,h4ck3rm1k3/shotwell,abrauchli/shotwell,jimbonator/shotwell,ritchiewilson/shotwell,jof/shotwell,Sanva/shotwell-gsoc,damianmoore/shotwell,polymeris/shotwell