git-link is no longer maintained and browse-at-remote has support for
more remotes.
- Bind '<leader> g o h' to open homepage in browser
- Rebind '<leader> g o o' to open file or region (omits the #L<N> suffix
if no selection is active).
Should also fix void-function/void-variable errors caused by evil-magit
depending on the newer version of magit (#1174).
Also introduces a redesign of the SPC g prefix.