libcolord: Load the profile defaults when using cd_icc_create_default()

This prevents a crash with LCMS 2.6 when we try to write a profile with no version.
libcolord: Add cd_icc_get_context() to get the internal cmsContext used by lcms2

We need this when calling native functions outside libcolord.
trivial: Fix a small memory leak when using cd_spectrum_get_value_for_nm()
trivial: Fix a small memory leak when using cd_icc_utils_get_coverage()
libcolord: Fix a potential crash when destroying a CdIt8 object
trivial: Fix up a small and large memory leak in the self test program
trivial: Fix a small memory leak when scanning folders of ICC files
trivial: Fix a tiny memory leak when writing MLUC tags