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.
Base pot update
I <3 run this from shell: php index.php generate
Adding support for percentage factor of additional costs.
update inline documentation in content-product.php and content-single-product.php
fixed indentation
added editorconfig
Updating woocommerce-admin es_ES
Ignore all log files except for .htaccess
Check for strlen to allow 0 values in attributes. Closes #3675

Conflicts:
	admin/post-types/writepanels/writepanel-product_data.php
making sure the user doesn't submit garbage to woocommerce_sort_product_tabs
removing html decoding from email from name
Minor Dutch translation bump, we need GlotPress
fix doc label to correctly point to woocommerce_before_single_product_summary
Merge remote-tracking branch 'upstream/master'
If is executed from shell, generate output for shell. ;)
Merge branch 'master' of https://github.com/rnt/woocommerce
Merge pull request #3710 from drrobotnik/doc

correctly point to woocommerce_before_single_product_summary
Merge pull request #3686 from GeertDD/ignorelogs

Ignore all log files except for .htaccess
Pass instance of WC_Order to its filters

So that extensions hooking to the filters know which order the current
filter is being applied to and can perform customisation on specific
orders (not just all orders).

Conflicts:
	includes/class-wc-order.php