Ability for User to Invite Specific User to a Group

[jterps08]

Currently, User A has the ability to go to Group X Profile page and invite all User A Followers to join Group X. We need to expand this so that User A has the ability to invite specific followers to join the group. User A should be able to type in User B's name/username into search field and send invite to that particular user.

[igaponov]

https://api-dev.powerli.ne/api-doc#put--api-v2-groups-{id}-invites