Add hooks for overriding default email inline styles

Currently any h1, h2, h3, a and img tags in a HTML email without a
style attribute will have a default inline style applied to them.
These styles are hard-coded and cannot currently overridden without
patching the source code.

This commit adds two filter hooks that allows the theme developer to
override both the list of tags that have a default style applied to
them and the default styles applied to each tag. The hooks are:

1. woocommerce_email_style_inline_tags
This filter hook returns an array of tags which will have a default
style applied to them - you can both remove and add any tags which
you need for your theme's custom emails.

2. woocommerce_email_style_inline_{name}_tag
This filter is called for every tag name returned by the filter hook
woocommerce_email_style_inline_tags. The styles are passed as an
associative array so you can both add and remove any of the default
styles applied by WooCommerce.

Fixes #3597.
Date format error fixed

Previous format displayed (when the timezone is set to America/Tijuana):
Martes 20th dAmerica/Tijuana agosto 2013, 05:53pm

New format displays:
Martes 20 de agosto 2013, 05:53pm

Adding .st, .nd, .rd, .th next to the number is not correct in spanish.
Adding BGN currency and currency symbol.
Some language corrections.
download icon
adding Vietnamese dong currency
Merge pull request #3661 from BFTrick/add-vietnamese-currency

Add Vietnamese Dong Currency
Merge pull request #3659 from dimitrov-adrian/patch-3

Some language corrections.
Merge pull request #3656 from dimitrov-adrian/patch-2

Adding BGN currency and currency symbol.
Merge pull request #3655 from ecoreng/patch-1

Date format error fixed
Adding Bulgarian states.
Merge branch 'Re-organise-settings'

Moves settings together. Fixes #3497
Moved options around for checkout settings.
Key value pairs for order_meta
Fix fatal error when sending order mail
Merge pull request #3665 from dimitrov-adrian/master

Adding Bulgarian states.
Addon layout fix
escaping
Echo or return current page title. Closes #3660
Make logout an endpoint. Still hide it from menus. Fixes #3589

@coenjacobs do we need to do something about this for .14? Will leave
for you next week :)