Initial implementation of LabelObjectText.

Still needs a lot of work.
Hook up object editor controls to text object.
Additional text object cleanup.
Added parsing of text objects.
Fixed several assertions and removed old diagnostic prints.
Write text object to glabels file.
Refactoring of text object code.  Autosize object unless size explicitly set.
Added ellipse object.
Box and ellipse subclassed to shape object.
Make sure object is unselected before deleting.
Reconcile coding style of dup methods.
Added line object support.
Install schemas.
Added image object support.
Initial porting of libglbarcode to VALA
Initial implementation of barcode object.
Added native support for UPC-A.

This is a proof-of-concept for the extensibility of libglbarcode.  Some
minor cleanup too.
Better parameterization of base font parameters.
Don't process non-existant templates.
Added EAN-13 support.  Assorted cleanup.