Documentation-only update: enableSwiping

Add enableSwiping option details to usage. I neglected to do so when I added the feature.

Fix tab disabled toggle not working

Fixes issue #27

Add option for custom scroll arrow content

Add leftArrowContent, rightArrowContent options so scroll arrow HTML can be customized.

This fixes issue #15.

This plunk shows how to use custom svg icons for the arrows:
http://plnkr.co/edit/2MdZCAnLyeU40shxaol3?p=preview

Add enable swipe option

Add option to allow horizontal swiping of tabs on touch screen.