Because if not, we may run out of the 16-bit integer space to store
reference count.

This was unnoticed so far as both Writer and Word output \pagebb instead
of \page when exporting page breaks.

There was still not enough space for German traslation

* cppheader.xsl had initially been written under the false assumption that a
missing oor:nillable attribute defaults to "false" instead of "true".  That has
been fixed.
* As a result, many places that use the new simplified officecfg/*.hxx headers
broke as they did not expect value types to be wrapped boost::optional.  To keep
the code simple, I decided to change all occurrences in
officecfg/registry/schema/ of properties that specify a default <value> and do
not explicitly specify oor:nillable="true" to oor:nillable="false".  Strictly
speaking, this is an incompatible change, but in many cases it should be what
was intended, anyway.
* Some places that use the new simplified officecfg/*.hxx headers still had to
be adapted to boost::optional wrapping.
* This showed that unotools/configuration.hxx did not yet work for those wrapped
properties and needed fixing, too.