Add lodash to bower.json

Lodash is a helpful utility library, similar to Underscore.
Add part_ids to hint table and hint editor, set part_id in API calls.
Render hints that have been sent to a student.

Depends on SockJS session being active.
Allow actually assigning StrugglingStudentFilter

Make sure to submit something for trigger_cond, even if it's empty. This
shouldn't really be required but eh.
Merge branch 'master' of github.com:yoavfreund/Webwork_AdaptiveHints