gscreen -fix early setting of states from preference file

dro_units, dro_absolute and toolsetting style were set from
the preference file outside of the usual preference file
function call, so could not be overridden from a skin properly.

eg with an missing preference file, dro_units would be set false
so any checks later of the preference file, would see that it is
false. Gmoccapy wants this True as default and could not do so.

Now by adding code to initialize_preferences() in the skins
handler file, the skin can have any default they want.
gmoccapy - fix imperial-as-default-preference bug

With an empty prefence file the default dro_units was imperial.
This left Gmoccapy with jogging in imperial units but the rest of the display
in metric.
This fix has been preceded by a fix in Gscreen to allow it.