More icons [backend].

This adds all Glyphicons Halflings that ships with Bootstrap v3.3.1.0. It also provides a more declarative way how to extend and map icons so custom icons can be used.

This also solves issue #5742 and skip need to change `link_to_with_icon` helper that is actually only one method that use custom icon namespace. Now all icons can be set from CSS and extended if other icons desired (like in many extensions).

Add 2 new aliases: 
- `money` using dollar/usd sign (should we not use Yuan? its the no1 economy today ;)).
- `translate` using globe (flag already default, but it looks more like a "way-point").