Add last_read information
Update change log
Fix:
 + display correct last read in format: MM-dd-YYYY hh:mm
 + refresh last_read when come back from meme detail view
 + refresh meme list and hide button after choosing meme source for the very first time the app initializes
 + zoom issue that constraint height of UIScroolView for the image whose height is less than screen height.

Add:
 + double tag to reset zoom scale level
Fix:
 + Change color of memeTitleBar at the bottom of screen.
Add:
 + Allow custom size of UINavigaitonBar button

Fix:
 + Respond to Choose Meme Source Button