Improve the workspace panel

The workspace panel could use some improvements:

• Inform the user of an existing invitation to join and allow him to view it.
• Display the membership type of the workspace and display an action label that corresponds to the membership type, just like it is done for the Workspace Directory actions (ex: "Request Join" or "Cancel Request" if the workspace is in request mode, etc.)
• Randomize the members avatars
• Limit the number of displayed member avatars to 3 rows (12 avatars)