build: s/gobject/gobject-2.0/

Corrected package dependency in cpml-1.pc.
adg: split AdgParamDress from AdgDress

Improved handling of dress parameters by using a more conventional
approach (directly borrowed from GLib). Moved dress parameter handling
on its own source files to reduce clutter.

This solve a number of warnings raised by gtkdoc-scangobj with the
previous commit.