This brings it in line with the default for other LibreOffice
components (e.g. Calc), or with the only supported value (e.g. Writer
tables), respectively.

Configure Pentaho jfreereport to also take null date == 1899-12-30

This combined allows reportbuilder to make absolutely no fiddly
conversion itself, leaving them to jfreereport and Writer table
cell format.

Also:

 - Make absolutely no conversion itself, also e.g. for booleans.

 - ODF compliance: make the value-type match the set foo-value attribute.

 - Use value-type="void" instead of empty value-type="string"

Change-Id: I67990232dbc9e86ac3fa37cd0c20edecb87cf8ee