Release of 2.1.0

Release for the migration to gtk 3.0

IMPROVEMENT: Migrates the application to the new gtk 3.0 framework.

UPDATE: Removal of GSEALED checks on gdk due to assumption of gdk 3 being
sealed.

BUGFIX: Allow LDFLAGS to be specified on command line.

BUGFIX: Fix compilation error for the mac port.

BUGFIX: Removed deprecated gtk / gdk function calls - thanks to dimstar