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)

Conflicts:
	localwiki/main/urls.py
	localwiki/main/urls_no_region.py
	localwiki/maps/views.py
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

Conflicts:
	localwiki/maps/static/olwidget/js/sapling_utils.js
Fix mobile CSS
Actually restrict the PageTagSet to the slug!
Link global tag pg from nearby tags area.

Conflicts:
	localwiki/themes/sapling/assets/css/site.css
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.

Conflicts:
	localwiki/maps/static/olwidget/js/sapling_utils.js
Fix global tagged page.