feat($animateCss): add support for temporary styles via cleanupStyles

[matsko]

Some animations make use of the from and to styling only for the
lifetime of the animation. This patch allows for those styles to be
removed once the animation is closed automatically within $animateCss.

---

This demo showcases a clear need for this feature:
http://plnkr.co/edit/uuTz4eudDvKgspOowEPm?p=preview

Notice how we need to do cleanup work once the animation is complete by removing the height property:

$animateCss(element, {
  from: { height: '0px' },
  to: { height: height + 'px' }
}).start().done(function() {
  element[0].style.removeProperty('height');
  done();
});

With this new feature we could turn the code above into this:

$animateCss(element, {
  cleanupStyles: true
  from: { height: '0px' },
  to: { height: height + 'px' }
});

[gkalpak]

Too long lines :(

[petebacondarwin]

This LGTM in general. I wonder if a next step could be to refine the cleanupStyles option to take a hash that would let you be more fine grained about what styles are temporary and what are permanent or is that never going to be needed?

[matsko]

@petebacondarwin I can see a use for that, but I don't want to bloat the API too much. Is there an animation that you can think of where this would be useful?

[IgorMinar]

let's keep the api simple for now. we can always expand it later via optional hashValue.

assuming all the other comments are resolved, this looks good to me

[matsko]

Landed as e52d731 for 1.4.x and 9f67da6 for 1.5.x.