[JBIDE-15666] Missing SSH_URL and Cartridges properties when reading Gea...

...r(s) in GearGroups

Added both properties
The cartridges returned by the IGearGroup#getCartridges() method are the one that
already exist in the parent IApplication. No need to create another subclass
of BaseCartridge, and the returned collection contains both IStandaloneCartridge(s)
and IEmbeddedCartridge(s)
The GearGroups collection is always refreshed because it is not cached in the ApplicationResource

Added unit tests to cover the parsing