invites/invite_room to return the user id not profile id

When searching for users in InvitesController#invite_room it was returning
the id of the user's profile but it should be returning the id of the user.
Remove html tags from private messages in the home page, fixes #812

Cases that use first_words() to get just a part of a private message's title
or body now also remove all html tags from the text to prevent unclosed
tags.