Create model for User and Tweet data
Some bugs to resolve
Fix cache error
Refactor TDAuthorsTableViewController
Remove attribute with type of number as id, in favor of id_str.
Update TDTweetsTableViewController for new TDUser model
Cahce image using SDWebImage
Amend last commit
Add load image method to TDUser
Refactor the logic to update author info, profile image, refresh table
Improve the encapsulation of TDUser
Recursive loading home timeline; sort author by tweets
Create singleton manager of core data context
Add account entity, refactor user model
Cache Tweets accordingly
Fix issue of invalid since id
Update tweets table view to display tweets
Clean up logs
Merge branch 'backend/cache'