Define facility classes hierarchy to encapsuate assignment and job
tests.

Commit ffba16f7 incorrectly renamed both
whoring related skills (whoreSkill and skillW) to skill.whore, while the
correct map is:
whoreSkill -> skill.whoring
skillW -> skill.whore

This commit restores skill.whoring attribute, partially fixing #657.

Put all attributes that hold counts of various actions, performed by
slaves, into the .counter sub-object in the SlaveState.

Various skills properties get moved into a .skill object inside the
SlaveState class.

Various porn.+ properties get moved into a .porn object inside the
SlaveState class.

This reverts commit 6b82f01e.