Set default to "Do not write out synthetic population"

[moeckel]

While it is useful to be able to write out the synthetic population for selected years, the default should be that the synthetic population is not written out. Currently, it is hard-coded that the final year's synthetic population is written out. The default shall be that no synthetic population is written.

We probably need a new property token: "years.to.write.out.syn.pop"

As a default, this property should be set to "-1", which means that no years are written out. The token can be set as an array to indicate, which years shall be written out, such as "2010,2020,2030"

[moeckel]

This should also make the property "print.out.sp.final" obsolete.