Add StickyGridHeaders dependency.
Use sticky section headers on activity screen.

Context menus and check-in buttons do not work, yet.
TraktTask: clarify which tvdb id is needed.
Add uri constructor for int TVDb id.
Fix activity check-ins by simplifying check-in dialog newInstance.
Activity: Put check-in context item first, like in other places.
Merge branch 'activity-sections' into beta