Feature/seletable title more like select2

[``* `#8743` Query select menu does not work exactly like select2``](https://www.openproject.org/work_packages/8743)

Wondering if it might have been easier to have just of used select2 instead of basically re-implementing it. Never!

[Note - "...to have just of..." is a tired scottish guy trying to say "...to just have..."]
ok you're right it's messy. i'll clean it up with clearer names and such like.

one of the reasons the names are unclear is because i'm trying to keep it generic ie could be any number of groups which contain any sort of object not just queries. having said that the template for this directive is full of references to queries so i haven't actually achieved this goal.