Manual set quality

I added a new section in Attribute to describe the alarm quality factor being automatically set (I called it automatic alarm handling) in the first commit. In the second commit, I added a sentence to allow the cppTango (and perhaps JTango) optimisation to not consider attributes without alarms configured when determining if dev state should be ALARM. These two commits are intended to describe how things work now.

The third commit adds the proposed changes to allow a set_manual_quality function to be implemented and the forth commit requires that attributes where set_manual_quality has been called to be considered when calculating dev state.

Closes #177 (closed).