Differentiate notifications

[franck-boullier]

Make sure that we have proper notification when cases are updated.
We are creating 5 different types of notifications

• case_new
• case_updated
• case_assignee_updated
• case_user_invited
• case_new_message

These notification types are described in the BZ table ut_notification_types

This is needed so we can do:

• Simplest notifications - A New user is invited to a case -> Notify the invited user
• Simplest notifications - The user assigned to the case is changed -> Notify the new assignee
• Simplest notifications - A new case is created -> Notify the Assignee

This is also a pre-requisite so that we can tackle:

• Weekly email digest to user about case activity
• Notification when an existing user is invited to a case (new or existing)
• Notification - Update the Notification page in the MEFE
• We need to enable notification when a case is updated