Added ActionBar, its documentation and icons
Added with_previous property to ActionPrevious
Added Bug Fixes
Corrected kivy image. Added '.png' to the file path
Reduced Size of action_item.png, action_view.png and textinput.png to make only one default theme image
Merge branch 'actionbar' of https://github.com/abhijangda/kivy into abhijangda-actionbar
wip
actionbar: remake styling by forcing the height of the actionbar, add ActionButton.icon, prefer icon usage instead of text when the button is not in a group, and various size fixes on images and button/icon.
merge actionbar
actionbar: update example