Cmake general reworking

[roccoarpa]

This pull should :

• resolve #137
• resolve #157
• resolve #166
• resolve #130 (cross referenced in #137)
• resolve #160 pool of issues.

READY bitpit pull https://github.com/optimad/bitpit/pull/117 merged

tasks done:

• [x] add Windows Mingw guide
• [x] add FindCGNS for automatic search
• [x] add FindMETIS/FindPARMETIS for automatic search
• [x] add OpenFoam automatic search for ESIOpenCFD v1906+ and OpenFoam Foundation 7
• [x] Cmake project updated and aligned with bitpit
• [x] Big simplification of the main CMakeLists, collecting functions and macro in reusable cmake packs.
• [x] introduced functions to handle deprecated/experimental features.
• [x] introduced LTO - Link Time Optimization (as in bitpit) to speed up compile time, at least for shared lib cases.
• [x] when mimmo is embedded in external projects force binding its twin compliant bitpit installation without asking each time the end-user to provide also the cmake installation path of bitpit (done in MIMMOConfig.cmake.in)
• [x] provide functions(cacheVarCleaners) to clear cache variables from other external packages polluting the current mimmo_package set up
• [x] aligned with new features introduced in https://github.com/optimad/bitpit/pull/117

Compliant with bitpit master @ https://github.com/optimad/bitpit/commit/ed4a93ea5e545c82abb7c15d195ba1250a6de2ba

AFTER MERGE Compliant with bitpit-master @ https://github.com/optimad/bitpit/commit/ed4a93ea5e545c82abb7c15d195ba1250a6de2ba

[roccoarpa]

Waiting new merge of https://github.com/optimad/bitpit/pull/117 for scheduling new modifications to be done.