Adds 2 pts on left padding of the text view by default
Fixes view constraints when no left button is configured
Updates constraint constants in -layoutIfNeeded instead, fixing a few update glitches
Uses textContainerInset instead of contentInset property, for adding left padding to the textView. Adjusts the placeholder label based on the left textContainerInset too.
Fixes left view constraint when the left button is not configured.
Avoids the keyboard to be dismissed during the navigation controller's "swipe-to-pop". Fixes #27