This creates the ability to make the User component send HTML emails instead of plain text.

We can override the registration and activation email bodies via the language overrides. However, any html markup does not work in the current Joomla release.

This PR adds a Send As HTML option in the Users global configuration to allow html in these email bodies:

Backwards Compatibility

When you switch the Send As HTML on, all emails not using html will still work.
The plain text email bodies use \n for new lines. These will be converted to <br /> tags (if no other html closing tags are found).

Testing instructions

To test this, create a language override for one of these language strings (depending on your settings):

COM_USERS_EMAIL_REGISTERED_BODY
COM_USERS_EMAIL_REGISTERED_BODY_NOPW
COM_USERS_EMAIL_REGISTERED_NOTIFICATION_TO_ADMIN_BODY
COM_USERS_EMAIL_REGISTERED_WITH_ACTIVATION_BODY
COM_USERS_EMAIL_REGISTERED_WITH_ACTIVATION_BODY_NOPW
COM_USERS_EMAIL_REGISTERED_WITH_ADMIN_ACTIVATION_BODY
COM_USERS_EMAIL_REGISTERED_WITH_ADMIN_ACTIVATION_BODY_NOPW

In this example I am using the settings: New User Account Activation: Self and Send Password: No.
So the language string to use is: COM_USERS_EMAIL_REGISTERED_WITH_ACTIVATION_BODY_NOPW

So you can create a language override for this string with:

<div style="background-color: #ededed; border: 1px solid #ddd; padding: 12px;"><h2>Your user account needs activating</h2><p>Hello [[%1:name%]],</p><p>Thank you for registering at [[%2:sitename%]].</p><p>Your account has been created and must be activated before you can use it.<br>To activate the account select the following link or copy-paste it in your browser:<br>[[%3:url%]]</p><p>You have registered on our site using the username <strong>[[%5:username%]]</strong>.</p></div><p style="font-size: small; color: #999; text-align: center;">You are receiving this automatic email message because you have registered at [[%2:sitename%]].</p>

Or add this directly to your en-GB.override.ini

COM_USERS_EMAIL_REGISTERED_WITH_ACTIVATION_BODY_NOPW="<div style="_QQ_"background-color: #ededed; border: 1px solid #ddd; padding: 12px;"_QQ_"><h2>Your user account needs activating</h2><p>Hello [[%1:name%]],</p><p>Thank you for registering at [[%2:sitename%]].</p><p>Your account has been created and must be activated before you can use it.<br>To activate the account select the following link or copy-paste it in your browser:<br>[[%3:url%]]</p><p>You have registered on our site using the username <strong>[[%5:username%]]</strong>.</p></div><p style="_QQ_"font-size: small; color: #999; text-align: center;"_QQ_">You are receiving this automatic email message because you have registered at [[%2:sitename%]].</p>"

The resulting email will look like: