Removed iOS 6.x warnings.
Deselect previous / next buttons after pressing them.

This fixes a lot of weird issues related to the prev / next buttons
state that would cause one or both buttons to not be active. Instead,
they'd be in a defunct selected state.
canTakeFocus now returns NO if element is not enabled.

This fixes an issue where the previous / next buttons would still
select disabled elements.
Merge pull request #428 from bartvandendriessche/features/disabled_elements_cant_take_focus

canTakeFocus now returns NO if element is not enabled.
Merge pull request #427 from bartvandendriessche/bugs/prevnextbuttons

Deselect previous / next buttons after pressing them.
Merge pull request #419 from tciuro/master

Replaced deprecated symbols in iOS 6.x