Improve usability of "Send Mail to Contacts" form and add support for CC and BCC

Add support for CC: and BCC: to the Send Email form - so it more closely matches users' experience / expectation from an email client.

1. By default, the To: field is populated with selected contact(s). User can enter additional To: recipients by adding a comma and starting to type another contact name (auto-complete). This way the Send Email activity can start w/ 1 or a group of values in the "list" (if I trigger it from a contact record or from a search result set).

2. Links to 'Add Cc" and "Add Bcc" are included just below the To: field. When cicked, the corresponding field is shown with the auto-complete / comma separated recipient list functionality.

3. The email form should work without a recipient passed in on the URL (i.e. if no cid= is included, then the To: is empty)

4. The auto-complete select contact widget used in To, Cc and Bcc should filter out contacts who we will not send mail to:

• Do not email = true
• Email address is on hold
• Contact is deceased