If user selects Email activity type as new activity from Manage Case, load the Send Email form instead of the regular activity form

If a case type configuration file includes 'Email' as a valid activity type - and the user selects this type from Manage Case -> New Activity dropdown, we should redirect them to the Send an Email form. The resulting email should be included in the case activity listing, in the same manner as emails sent by clicking the email icon next to a Case Role.