Add page-label attribute to pagination directive

[ashaffer]

The page-label attribute is an expression that returns a label given a page index (in the scope local $page).

This is a fix for issue #2532

[nikitiuk0]

+1 for this. can someone please merge it and release a new build?

[shawnzhu]

This is a good use case for this feature: add text instead of numbers in pagination, angular-bootstrap

[michael-wirth]

1+

[wesleycho]

Going to close this due to it being outdated - feel free to file a new PR against current master with the updates to be in a mergeable state.