pygr.helper: Provide independent ColorIndexGenerator instances.

- ColorIndexGenerator provides one staticmethod nextColorIndex() which returns
  the next color (index) independent of any instance.
- getNextColorIndex(self) returns the next color (index) for the given
  instance. Every instance provides its own and independent counter.
pygr: fix x/y alignment for xlabel and legend items

Fixes: #1292 https://trac.frm2.tum.de/redmine/issues/1292
pygr: Support more than two legend item rows.

The viewport size will automatically be adjusted if a legend item cannot
be displayed inside the current viewport.
pygr.helper: Reset index on ColorIndexGenerator instances.

- reset(self) sets the internal index on the first color (index)
  for the given instance
Changed Pascal floating-point precision to double
Build Pascal demo for x86_64 architecture
Merge branch 'master' of ifflinux:gr