Now always remove the radial component of velocity from the GPlates plugin.

Before the removal we check that this component is small, to ensure the rotation and projection is working properly. If it is small and we do not want to have it in the solution we might as well remove it completely.
Add an assertion.
Add a test for the existing GPlates plugin.
Implement patch for GPlates 1.4

The patch checks for the version of the provided gpml file and also
includes an assertion against creating an unreasonable mesh.
Add test for the new GPlates 1.4 patch.
Update the manual for the GPlates 1.4 patch.
Updated changes.h.
Improved the version check for gplates.
Another bugfix for gplates version check.
Merge branch 'gplates-1.4-patch' of https://github.com/gassmoeller/aspect

Conflicts:
	doc/modules/changes.h

https://github.com/geodynamics/aspect/pull/73