[cmake,release] Install cmake macros to $(datadir)/dune/cmake/

Previously, the macros were installed to $(datadir)/cmake/. As we have
some macros in DUNE that might also be in other packages
this may cause conflicts in package managers. With this patch we install
them to $(datadir)/dune/cmake to resolve this issue. Together with the
last patch this will resolve problems  outlined in flyspray
task 813
https://dune-project.org/flyspray/index.php?do=details&task_id=813
I apologize for givin the wrong task number in the previous patch.
(cherry picked from commit 5dd5e16062c73f66d3fa210e947a866def5010d7)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[cmake,autotools,release] Complete the last 2 patches concerning macro installation path.

Somehow I missed some files when committing. this patch fixes this.
(cherry picked from commit 2e987422796620cbad5387930754c7b0cefa59c7)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[cmake,release] Makes macro installation path adjustable.
(cherry picked from commit aeca0428f82cf4f49eaa02765fdef11826caafa2)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>