Added "removed" feature type

"Removed" features and "deprecated" features look the same except the tooltip content is different.

BUG=#100

![screenshot from 2014-07-17 13 28 34](https://cloud.githubusercontent.com/assets/634478/3612118/b1368004-0da5-11e4-9ecf-b1b3656f69fb.png)

we can probably simplify this a bit:
 
    <span hidden?="{{!removed && !deprecated}}" class="tooltip" title="{{removed ? 'Removed feature' : 'Deprecated feature'}}"><i class="icon-warning-sign" data-tooltip></i></span>