Limit display to only whole integer values for relative date formatting in main chart
x values for charts now moved to centers of time intervals.
chart interval updates
Merge branch 'master' into chartAlignment
All minicharts are now aligned on x.

Keep in mind that this sacrifices some viewing space horizontally.
To avoid that problem, we could add a single range navigator somewhere
(like the one in highstocks) to control the x zooming for all the minicharts.