Bug #805780

Adds a logo field to the institution edit form.  On upload, the file
is saved as a 'profileicon' artefact, to ensure that it's publicly
visible, and can be requested in multiple sizes by thumb.php.

Change-Id: I7ea50f75b6e5fed8043c5cd9812e82809a6ef600
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>