Rename genericgeometrypage to referenceelementspage

And move it from the special genericgeometry documentation directory
to the normal module documentation directory.
(cherry picked from commit 882ba5177142b290a1ace171ae885893a52f5891)

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>
Remove doxygen page genericgeometrytransitionpage

This pages explains how to port code to the reference elements constructed
from tensor and conical products (i.e., the 'generic' reference elements).
It is very old and outdated, and only serves to confuse people nowadays.
(cherry picked from commit 72cb0baf671b27ffbc319e0ef763cfe263850c67)

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>
Remove one tab.  This make images appear again.

Don't ask me why.
(cherry picked from commit 603444deb8382e306bb541bfffcf31a4b79a6425)

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>
[cleanup,documentation] Remove the 'generic' prefix from various doxygen labels
(cherry picked from commit 8e8d580da2ac11e71d0501b22847a199de65d028)

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>