Add support for timestamps with millisecond resolution.

I'd rather do microseconds, but sadly javascript timestamps don't support
it. :(

Change-Id: I2db336a170722f8fbd44f51fcd3c47b9df011ccd
Convert T_NUM column data to actual numbers at import time.

Otherwise dygraphs gets confused if these are the X axis.

Change-Id: I2cf267550f4f4a70006c50b3482a3cc46907c90a
Add traces+minmax mode.

- Also greatly improve speed and accuracy of rendering the crosshairs.
- Improve how we display Y axis labels and chart names (though it's still
  not that great)

Change-Id: I63a3df4fa3d1699bc0f3243a315c8b5d9b3f333d