Images: Rolled out image memory handling to image actions

Images: Rolled out image memory handling to image actions

- Moved thumnbail loading out of repo into ImageResizer.
- Updated gallery and editor image handling to show errors where
  possible to indicate memory issues for resizing/thumbs.
- Updated gallery to load image data in a per-image basis via edit form
  for more resiliant thumb/data fetching. Data was previously provided
  via gallery listing, which could be affected by failing generation
  of other images.
- Updated image manager double click handling to be more pleasant and
  not flash away the edit form.
- Updated editor handlers to use main URL when thumbs fail to load.