subtree and class filters on autocomplete

These changes add the possibility to filter autocomplete results by subtree and / or specific classes.
The changes also include modifications on css that allow having an autocomplete features added to the search input of the edit form of object relation and object relations attributes
I have sent a pull request on the ezpublish_legacy repository for the object relation(s) modifications:
https://github.com/ezsystems/ezpublish-legacy/pull/620
not blocker, but: space between previous block