Fixes for map clustering.

Fixes up map clustering on Map-for-tag pages.
Merge branch 'interim_splash_site' into global_tags
First draft of global tags.

Currently, there is no discovery mechanism for the global tags.

Also lacking:
   * Proper formatting on tag list page
   * "Nearby tags" when viewing a tag on a particular region
   * Links from search page (global search)
Link global tags from global search page.
Better formatting on global tag list page.
Suggest global tags when adding tags.
Simple 'Other nearby pages' on region tag page
Fix mobile CSS
Actually restrict the PageTagSet to the slug!
Link global tag pg from nearby tags area.
Nearby map link to global map
Global tags support w/ meta regions
Fix /<region>/tags/ page layout.
Fix included tag + map CSS.
Some tag 404 handling.
Don't cluster map tags on all zoom levels.
Merge branch 'global_tags' into interim_splash_site