[FIXED JENKINS-22686] Add a few pixels distance between tick labels.

Because *this* isn't that easy to read:

![Screen shot](https://cloud.githubusercontent.com/assets/1831569/2749434/b34540fe-c801-11e3-9f46-121614111385.png)

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### PR notes

**Update**: Updated PR to determine margin from size of the label instead of hard-coding pixel count.

While for the `MultiStageTimeSeries`, only right margin would be needed, I added all four, as the rest of the code also supports other orientations. The left margin is useless (except for consistency) though, could leave that out if it bothers someone.