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
Merge branch 'branch-v2' into branch-v2-layout-tweaks
Thumbnails as default at spaces/index and small layout changes in it

Changing the place where the buttons to select list/thumbnails and the button
to create a new space are placed in this page.
List of activities link in the header of users' homes
Show past 5 activities instead of 3 in users' homes
Crete standard form to report spam for events and posts

For posts it was already ok, but for events wasn't working. Now they use the
same partial to render the form.
The actions to create spam reports were also modified to make more sense.
Better layout for spam icons on posts and events