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.
Adding support for percentage factor of additional costs.
Remove echo
Fix from .14
Added "Demo Store" Class to Body

Adding "woocommerce-demo-store" class to body when option
"woocommerce_demo_store" is enabled.
(Handy to push down content to allow for banner, etc.)
Merge pull request #3730 from lucanos/master

Added "Demo Store" Class to Body
Missing line break in email Closes #3727
Added .14 readme to 2.1 master
Bulk/quick edit backorders Closes #3729
Update CA.php

Correction for Newfoundland and Labrador Province abbreviation : http://canadaonline.about.com/od/postalservices/a/abbreviations-provinces-canada.htm
Show woocommerce messages in empty cart. Fixes issues when a message is queued to be displayed and user is redirected to cart page where he/she can not see any messages.
Filter user_has_cap with woocommerce_customer_has_capability
Check if user is allowed to cancel and order an order again. Use current_user_can() checks instead of hardcoded user_id comparisons to determine if user can view, pay, order again or cancel an order.
Use default priority for user_has_cap filter
Add download_file capability and security check
Fix missing semicolon
fixing unescaped character in date function
Update html-admin-page-status-report.php

Add update notification if theme is a WooTheme
View logs from System Status
CN translation by wang hong wei