Add Option for forcing thousand separator for stats counter block

[Gentyspun]

Epic: #417
Issue: #5

Adds a checkbox to the localisation tab inside Theme Options that forces the use of thousand separators on the stats counter block.

Steps to test:

1. Before checking out this branch, edit a post on /es/
2. Insert a counter block and populate with a number > 999 but < 10,000
3. Save and view the front end.
4. Notice the number will have no thousand separator.
5. Checkout this branch and run a build
6. Go to es/wp-admin/admin.php?page=amnesty_localisation_options_page
7. There should now be a checkbox for "Force Thousands Separator"
8. Check this, and save.
9. Now return to your counter block front end and refresh
10. The number should now display with a thousand separator (e.g. 3.445 for Spanish)

Considerations:

• Localisation

Example: http://bigbite.im/v/Rl4WKF