EOS from IDM

The EOS Number and unit description (and parent units) are now available in the IDM database.
Since `org_unit` and `eos_number` are equivalent (and thus redundant), they could be consolidated, i.e. combined in one field.

This opens other options:

- select institute from dropdown
- get the supervisor's org unit (at login) and pre-select their org unit as a default (changeable)

Caveats:
- Some users belong to more than one unit. The IDM API either gives back the "first" (by whatever order) or an array of all unit numbers (not sure)
- Some users may not be in the org tree