Update Bulgarian regions names and codes

Update Bulgarian regions codes according to ISO 3166-2:BG http://en.wikipedia.org/wiki/ISO_3166-2:BG and http://www.statoids.com/ubg.html
Also updated the region names be wrote with latin chars for more universalize and easy translated.
Removed duplicate description key. Closes #4357
replace a few missed &rarr;'s. closes #4350
Merge pull request #4347 from dimitrov-adrian/patch-8

Update Bulgarian regions names and codes
short description meta box #4356
checkboxes in product data tabs #4356
add gallery images link
Merge commit '05dda2c16a32375b3f831144d8c2ccb8cbe73ea1'

Conflicts:
	includes/gateways/paypal/class-wc-gateway-paypal.php