Standardize Infinite Scrolling Behavior

[jterps08]

We need to make sure there is standardized Infinite Scrolling behavior across the platform:

• The system supports endless crolling
• The app loads more items when the user gets towards the end of the list
• The app keeps the user in the same 'scroll position' when more items are loaded (user is not returned to top)... sticky scrolling

These are the screens that this principle should apply to:

1. The Main Newsfeed
2. The Social Activity Feed (You tab, Following tab)
3. The Item Detail Screen (specifically re: loading more comments)
4. The Discussion Screen (for child comments/replies)
5. The My Influences Screen (loading more users)
6. The Group Membership List Screen (loading more users)
7. The Favorites Screen
8. The User Profile Screen (loading more user posts)

[jterps08]

From #574: User scrolls to bottom of comments and the app correctly loads more, but returns the user to the top instead of keeping the user at the last comment he read.

User sees comments 1-10
User gets to comment 10
App loads comments 11-20
App returns screen position to comment 1 (wrong)
App should return screen position to comment 11 (correct)

This should be the behavior of ALL screens that have infinite scrolling:
My Influences
Social Activity Screen (both tabs)
User Profile screen (user's previous posts)
Newsfeed
Comments on Item Detail Screen
Comments on Reply Screen