Show spaces in the top of the user's home, refs #805

Also changed the way spaces are show in the user profile, now using the same
partial used to show spaces in the home pages.
Simpler user home and new /home/activity, refs #805

The user's home now shows only the top 3 new activities and there's a new
page (/home/activity) that shows the complete list with pagination and
everything.
Show space visibility in the list at users homes, refs #805

Show if the space is public or private.
Thumbnail list of spaces with same style as users' homes, refs #805