Begins implementing configuration UIs for each
source processor.

When the config dialog is opened, the plugin panel
is disabled for as long as said dialog is open.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>
Performs some major refactoring in various classes in order to
facilitate the loading and saving of processor settings. We use
GLib.Settings for this, along with an external gschema file.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>
Adds gschema file and modifies Makefile to have it be
compiled and installed along with the plugin code.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>