Restrict the displayed activities when clicking on "Email Marketing"
and "SMS Marketing" modules in the activity systray. Due to their
activities being linked to the same model, we need to distinguish which
activities belong to which module based on their assigned mailing_type
value. Without this domain restriction, users can still filter based on
mailing_type, but it is much less intuitive this way due to them being
separate apps.
Task: 2169498
Due to 'mass_mailing_sms' inheriting mailing.mailing from
'mass_mailing', activities for these two modules would show up as one
"Mass Mailing" line in the systray. This commit adds additional logic
to remove this "Mass Mailing" line and replace it with 2 lines: "Email
Marketing" and "SMS Marketing" with their appropriately matching module
icon. For consistency, when only the 'mass_mailing' module is installed,
it will still display "Email Marketing".
Task: 2169498
Tiffany Chang (tic)