Improve support for timeline data

[arnikz]

Currently, it's difficult to make a plot using the following data:

JobID,Start,End
4099110,2018-03-19T23:22:52,2018-03-20T15:33:33
4099111,2018-03-19T23:22:52,2018-03-20T00:46:57
4099112,2018-03-19T23:24:23,2018-03-22T09:42:58
...

where Start and End (or duration) of a job are on the x axis and JobID on y axis. My first approximation was to assign duration to the point size, resulting in a crowded plot with too many "bubbles". Ideally, one would like have a horizontal line (connected pair of start/end points) per job.