Engine: UI: Dashboard: fix loading of system group widget
Engine: models: fix some base class namespacing on models

Several of the models were referring to base class namespaces
(e.g. ::Provider); therefore, updating them to use the engine's
base.
Engine: UI: org-switcher: response should not be named object

E.g. the user object will not be returned as { 'user' : { ... } }
for the v2 api.
Engine: UI: fix ability to add/remove systems from system group