Added table and updated code to support loading services other than default. Updating this list is currently available only via direct access to database, so no GUI for now.
each service has assigned numeric ID, which is (and will be) used as identificator in database
added test to control, if service has all required constants and uniqueness of IDs
added class to maintain message settings (which services in links, which services in buttons and which service is used for screenshot)
Added table and updated code to support loading services other than default. Updating this list is currently available only via direct access to database, so no GUI for now.