Wrap ChamplainViewport

	* champlain/champlainmm.h: Add viewport.h.
	* champlain/champlainmm/.gitignore: Ignore viewport.*.
	* champlain/src/champlain_signals.defs: Add "relocated" signal;
	add "x-origin", "y-origin", "hadjustment", and "vadjustment"
	properties.
	* champlain/src/filelist.am: Add viewport.hg.
	* champlain/src/viewport.[hg|ccg]: New files.
	* tools/extradefs/generate_extra_defs_libchamplain.cc: Add
	CHAMPLAIN_TYPE_VIEWPORT, and include specific header.
	* tools/m4/convert_libchamplain.m4: Add conversion from 'const
	Glib::RefPtr<Adjustment>&' to 'ChamplainAdjustment*'.