stackdriver: make sure service and metric display name is used instead of value when loading a saved query editor

stackdriver: get value type and metric kind from metric descriptor instead of from latest metric result

stackdriver: break out aggretation logic into its own directive and controller. also adds tests for new dropdown population logic

so can reuse for annotation query ctrl.

We had incorrectly assumed that a service account could only be connected
to one project.

This is using the {{}} syntax for alias patterns. Might
switch to the  syntax instead.

Explore: Query field fixes

Fix misspelled authentication in Auth overview doc

Still have to figure out if we should have templating for aggregation
fields