Move to SI units - add polarization about magpylib HOT 2 CLOSED

What's happening on the core level:

NEW ARGUMENT ORDERS
- field
- observers
- position=(0, 0, 0),
- orientation=None,
- dimension / diameter / vertices / ...
- polarization / current / moment
- magnetization
- style=None,
- **kwargs,

CHANGES IN CORE FUNCTIONS:

• comment #CORE

• no more positionals, named arguments only ( *,... syntax)

• codependent magnetization <> polarizations

• variable order reflecting new order

• variable names in singular (again) - we can change this later if we want

• Top line in plural

• SI units are used for all inputs and outputs.

• rearrange Parameters

• everything SI: T, A/m and m

• fix computation to SI output: B is good, H=B/mu0

  • include MU0

• implement/fix tests

  • add self-consistency test B = MU0*H + J

• fix doc examples

• Notes: advanced units

from magpylib.

fixed by #712

from magpylib.