[test.gtest] disable warnings inside
[test] moved main_header.hh -> common.hh
[test] moved main_header.cxx -> common.cxx
[lib] update
[test.main] removed header guards (this is not a header)
[test] removed deprecated files
[test] updated includes
[test] removed empty fem_error
[test.common] updated include
[test.main] fixed includes
[test] updated includes