If equation is too long compared to chart width:
  equation is wrapped
  and if equation has General format, the number of digits is reduced

In this patch, only polynomial equation is treated. If this approach is ok,
I will extend to other regression curves.

Conflicts:
	chart2/source/view/charttypes/VSeriesPlotter.cxx

Change-Id: I1bfd897881d752655faec6df034c0dde7f78c51b
Reviewed-on: https://gerrit.libreoffice.org/18397Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>