Words missing from the dictionary/not recognized

## Description

The following words are not known to Harper (I'm using the British version at the moment) (unknown -> spurious fix):
- gray -> gay/grab/grad
- discretization -> discrimination
- ansatz -> ersatz
- Plasmas -> Plasma's/Plasma
- unmagnetized -> demagnetized/magnetized
- collisionless -> collision's collision
- isothermal -> isotherm/isotherm's/isotherms
- wavefronts -> wavefront/waterfronts/lakefronts
- bitangent -> tangent
- magnetohydrodynamics -> No suggestion
- collisional -> collision/collision's/collisions
- symplectic -> simplistic/apoplectic
- inhomogeneous -> homogeneous
- extremum -> extreme
- dimensionality -> dimension
- separatrix -> separate
- wavenumber -> renumber
- isotropy -> isotope
- rotationally -> rotational
- gyrofrequencies ->frequencies

More uncommon words and thus forgivable errors:
- heliosphere -> hemisphere
- magnetosheath -> magnetosphere
- magnetopause -> magneto's

Finally, this might be a grammar error? Not sure how to categorize it:
- This leads to a sum over all elements. -> This leads to a sum overall elements. (over all -> overall)

If you need anything else from me, let me know. I haven't looked into how to fix these things on my own. So if anyone else has the time to add the words to the dictionary/dictionaries, that would be fine by me :). Thank you for making this software open-source and available ❤