* extend RuleStore interface to get namespace by UID
* add new export API endpoints
* implement request handlers
* update authorization and wire handlers to paths
* add folder error matchers to errorToResponse
* add tests for export methods
* generalize error handling in forking request handlers
* remove MatchesBackend and change test to test Can
* add 404 to route specs
* change backendTypeByUID to getDatasourceByUID of expected type
* use common errors in api testing
* handle 401 in errorToResponse
* replace backend type error with "unexpected datasource type"
* update swagger spec
