#191 electromagnetic_filed and problematic subclasses

[Snezana Nikolic]

Something needs to be done with electromagnetic_field and couple of its subclasses:
|- electromagnetic_filed NEMO_1000000
|- electrodynamic_field NEMO_3510000
|- magnetic_field NEMO_0491000
|- electrostatic_field NEMO_0606000
Please see the ATTACHMENT which contains some arguments/proposals of what to do with them, and proposed definitions for these classes.

[Snezana Nikolic]