Fix several block issues.

* Allow multiple locations for users and nodes.
* Fix marker titles and give them sane values.
* Add offset to make markers with multiple images work as expected.
* Rewrite gmap_location_author_block_view() to work similar to gmap_location_block_view().
* Remove hardcoded 'gmap_location_authorblock' mapid to match the behavior of the node block. (Reassign it in the macro if you need it.)