Consistent content items UI states

- Selections now stay on the correct view when scrolling
- Animations are completely fixed in the sense that views are not delayed with animating when scrolling. Also, when scrolling, no random views are suddenly animating.
- The indication whether a file is being processed now works by checking the queues of the encryption service.
- (forgot to add in commit) Thumbnails should now be set more efficiently and hopefully will update nicely when loaded (some people were still getting blank thumbnails until pressed on an item)

Can't fix:
When selecting a file, and unlocking it, an action item unnecessarily gets thrown into a "..." element, but it won't open... Not sure how to fix this, seems like a bug.

Closes #157.