- extends handlers for panel menu and keypress 'x'
- in a mixed-datasource panel finds first datasource that supports
  explore and collects its targets
- passes those targets to the found datasource to be serialized for
  explore state
- removed `supportMetrics` and `supportsExplore`
- use datasource metadata instead (set in plugin.json)
- Use angular timeout to wrap url change for explore jump
- Extract getExploreUrl into core/utils/explore

Explore: Store UI state in URL

13411 react api key

Stackdriver Datasource - Fixes #6733

fixes glitch where an empty tag shows up

with dummy change in readme to be able to make a commit

Limit number of time series in explore

After discussions with the Stackdriver team, they did not think this was
needed.

Storing queries, split state, and time range in URL.

- harmonize query serialization when generating Explore URLs in
  dashboards (use of `renderUrl`)
- move URL parse/serialization to Wrapper
- keep UI states under two keys, one for left and one for right Explore
- add option to angular router to not reload page on search change
- add lots of types
- fix time service function that gets triggered by URL change

Grafana high availability (ha) test setup

stackdriver: broadcasting through $scope doesnt work anymore since query_filter_ctrl is now a sibling directive to query_aggregation_ctrl, so broadcasting is now done using $rootScope

Adding AWS Isolated Regions