Timestream interface improvements

[pszjmb1]

The following are little UI improvements I'd like to see for the timestream interface:

• It would be nice to scrub the playhead rather than clicking on points
• When adding start time for the first time the green area is filled in the wrong direction
• Previous and next button should be disabled when the end of the data is reached
• The y-axis should show the unit
• The x-axis should always show the date as well as the time
• Currently the previous/next buttons moves 500 points. It would be nice to be able to shift by less than that in some instances.
• The head time field should be filled in on refresh
• The start time and end time fields should show the same date/time format on refresh as when the timestream is clicked
• Users should be able to add context records by clicking on a timestream datapoint