Refactor: Modify CC address entries

[Samlant]

Description, issue

Currently there are two separate boxes for user to input CC email addresses. This makes it's purpose more ambiguous for users to grasp.

Solution

We can make into a Treeview (without a header), one column so hide the index col, add & remove buttons.

Alternatives

entry box for adding into a textbox, each separated by a new line; (currently) two text/entry fields;