Prevent a lot of sql queries for ProjectTeam#fetch_members method

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
More efficient query for mentionable users

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'performance-improve' into 'master'

More performance improvements for large groups

* fetch team members using much less sql queries
* collect mentioned users without iterating over all project users