[Rails] Allow community admin to change their community name

[rudokemper]

Currently, only a Super Admin can change the name of a community via the Super Admin Dashboard:

Let's make it so that a community admin can also change the name via the dashboard in the Themes edit view (/en/member/theme/edit)

Acceptance criteria:

• A logged in admin user of a community can navigate to the Theme edit view, and above "Welcome screen", sees a text box option with the label "Community Name"
• The label for the field should be using internationalization (both {community} and {name} are available keys).
• Upon changing the name, the community name is updated in all relevant places.