Feature/issue 191 autolist question

Closes #191:

Novelties:
* new "autoList" question type, where you can define a list of possibilities (with tags) that autocomplete what the user enters. You can select as many items as you want.
* if the user can't find what he wants, he can keep typing and add what he typed. Whatever he adds is kept for future completion in future probes (indexed by question name, so you can do that for different questions)

The design needs some uplifting. @Gislain I'll do a release this evening, can you do a design for this question?