Smarter presentation layer for time segmented graph information

[bmbouter]

Given that time data is reported back in milliseconds since the epoch, when segmentation uses a time based field, the graphs labels make no sense. This could be corrected in the following ways:

1. Have the graphing code recognize when a time-based field is on the x-axis
2. Have the user given a choice between "absolute" or "relative" x-axis labels. milliseconds since the epoch should be converted appropriately. The time scale should be seconds for both "absolute" and "relative" x axis labeling.
3. Not every point shall have its label be displayed because the labels run over each other visually. Omit labels on the x axis as appropriate for readability. This should be dependent on the number of points being displayed.

[omarestrella]

Commit 47ec285 includes a fix for points 1 and 2. A datepicker is currently implemented. Point 3 is a limitation of the plotting library and will be looked at soon.