With this change, the automatic y-axis scaling should be more accurate
for stacked charts (i.e. stacked line, area, bar charts) with dates on
the x-axis.  The previous algorithm only calculated the max and min
y-values of the individual data, without taking into account the stacking
type when the x-axis type was date.

Or else we'd end up drawing a pretty interesting diagram...

(With the insight that Data::components is RootNode::members.)

Triggered by fdo#43725, incrementing an invalid iterator bombs -
though this seems a corner case, depends on whether one considers
"+= 0" as incrementing or not.

 * some cleanup - removed ugly-as-hell exposure of only parts of the
   internal data struct on B2DPolygon (and reworked the only client
   of that code)
 * added stl-style begin/end to B3DPolyPolygon as well, mirroring
   B2DPolyPolygon, plus adapting the insert() func to make use of
   that (avoiding loads of temporaries)

Though it looks wrong that rtl_allocateMemory(0) == 0.

Add --bzip2 and --xz options to select the compression. Both options
can be used togetger to generate both types of tarballs in one call.
XZ compession is used by default.

Also renamed "lo*build" strings to "lo*core" to fit the current name
of the top level source directory.

Mimic Hungarian Excel's key bindings:

* inserting current date is Ctrl-'.'
* inserting current time is Ctrl-Shift-'.'