Debugged last IMAS changes to units

[Didou09]

Main changes:

There were 2 main issues:

1. IMAS does not have imasdef anymore, and instead uses imas.ids_defs to get the backend
2. IMAS has new built-in classes for arrays, scalar, str etc that tofu was not identifying

To address 1, the main useful changes were in tofu.imas2tofu._core.py

    from imas.ids_defs import HDF5_BACKEND
    try:
        from imas import imasdef
    except Exception:
        imasdef = None

To address 2: the main change happened in tofu.imas2tofu._com.py
tofu now reckognizes them and converts to the standard numpy, float, int, str

Issues:

Fixes, in devel, issue #1158