Create prompt for right-axis metrics

If there's two or more metrics, and they are all on the left, prompt the user
that they can click one to move it to the right.
Alerts div will have the class alert-danger, not the id
Allow both absolute and relative times for start/stop

Relative (or nice) and absolute (or seconds from epoch) times are now
interchangable in a machiavelli base url.

Cleaned up a heap of checking in the controller to suit. Utility functions in
the app helper to assist.