Replace jqeury.autosuggest with select2.

This replaces jquery.autosuggest with the much nicer jquery.select2 plugin. 

- Select2 has the advantage that the original dom element is used for the storage of the value. So no more messing around with additional fields and their special ids.
- It is also supports all kinds of special characters in tag values.
- Patterns integration is simpler with cleaner code.
- It coexists well with our input-change event translation and pat-autosubmit (which was the main incentive to replace the old plugin).