Check if keyboard is visible before animations

Check if keyboard is visible before performing animations on it after
UIGestureRecognizerStateEnded.
When the user swipes down too fast, the keyboard is no longer visible,
but jsq_handlePanGestureRecognizer:(UIPanGestureRecognizer *)pan still
tried to animate it.
contributing.md
properly handle in-call status bar. fix #219. remove legacy toolbar frame changing code that used to be necessary with DAKeyboardControl.
Returning early instead of large conditional block

In response to jessesquires pointers in the pull request issue_213_fix.
Compare using <= 0.0f instead of == 0.0f

Slightly more robust, in case the keyboard is ever positioned even
lower than the height of contextView.
Improved keyboardViewIsHidden calculation
Merge pull request #231 from koenbud/issue_213_fix

issue_213_fix - Check if keyboard is visible before animations
minor tweaks to keyboard controller
only dismiss keyboard if dragging down near input bar
disable keyboard interaction during dismiss
reset statusBarChangeInHeight on rotation. and dismiss keyboard. cc: issue #219
Update collection view insets and scroll to bottom when textView size changes
Only scroll to bottom on textview size changes when automaticallyScrollsToMostRecentMessage is set
Merge pull request #233 from andrewchae/version_5_offsets

Update collection view insets and scroll to bottom when textView size changes
improve rotation handling
clean up
data source docs
collection view delegate docs
collection view docs
collection view cell docs