This fix adds a signature forcibly if found under the sender's
User.email_signature or default outgoing email account's signature
field.
The previous method of adding a comment into the Email didn't work since
Quill would discard comments before setting them. Adding signatures in
get_formatted_html didn't seem apt since it's used in QueueBuilder to
re-construct the Email before processing the Email Queue. This meant
that the email content that was added in the Communication record would
not be final. Now, we treat the signature as part of the Communication
content.
* DRY font-family declarations
* Add email.less, inline styles using premailer
* min-width 100% for mobile email clients
* Emails without header have default 100% width (like before)
* Include email.css for all apps
* Keep !important declarations
* Add test case for inlining css
* Ignore important rules in css
* minor
* inline images working, ability to use template name for emails
* Extract header into separate file
* Remove erp-logo
* minor refactor
* [minor] codacy
* fix for test
* Add test case for email body
* remove unused imports
* Add more tests for email body
