Improved functioality and compatibility with different plugins

This pull request contains the following:

 - Added mentions for Luxury buttons textareas
 - Searches only return users that are members of a project
 - Email and simple `@` won't trigger a search
 - Added a limit for maximum characters in search (set to 15)
 - Modified regex to cover the login format used vor validation, related to #6
 - Links are added with full path in order to appear correctly in emails, related to #5 (also tested 1622e2e039ebbb2aaa68033e2eea6bd609e0de9e and it seems to work well so unles @rozzin has other problems #5 can be closed)
 - Integrated changes from 1cc846b33a404dfb032b0fd648289e69a7b2a25d for links in issue description 

I am not sure about the syntax in the .less and .scss files, that needs a second look.