Bug #1006634, part 3

Replaces existing group/view.php urls with calls to
group_homepage_url, in a bunch of places where only a minor change is
required to fetch the urlid property, and where it is clear it will
have little impact on performance:

- My groups block
- Cancel button on group delete
- Redirects after joining a group or inviting a user
- Group tab of the admin stats area
- My groups section of the profile sideblock
- Redirect after submitting a view

Change-Id: I0ab970bdc4aaefe9fb912f9e530ebe1684aed011
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>