Increased compatibility to API > 9

Hi,

I changed the tab bar such that it is also compatible with api 10 and higher.

Kind regards,
Pieter
Change for [ViewCompat.setAlpha(View, float)](http://developer.android.com/reference/android/support/v4/view/ViewCompat.html#setAlpha(android.view.View, float)) in the support v4 library