Hack around non-existing matrices for noncommutative rings (Fixes #419)

[thofma]

• AA does not have matrices for noncommutative rings (yet)
• We make our algberas/orders subtypes of Ring (to make matrices work)
• But we want NCPolynomialRing for polynomials over this ring

[codecov]

Codecov Report

Merging #441 (b66234f) into master (537adda) will decrease coverage by 0.05%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master     #441      +/-   ##
==========================================
- Coverage   66.43%   66.37%   -0.06%     
==========================================
  Files         303      303              
  Lines       90855    90854       -1     
==========================================
- Hits        60356    60307      -49     
- Misses      30499    30547      +48     

Impacted Files	Coverage Δ
src/AlgAss/AlgMatElem.jl	58.06% <ø> (+2.25%)	⬆️
src/AlgAss/Types.jl	72.38% <0.00%> (-1.10%)	⬇️
src/AlgAss/Elem.jl	81.31% <88.88%> (-0.18%)	⬇️
src/AlgAss/AlgMat.jl	80.06% <100.00%> (ø)
src/AlgAssAbsOrd/Conjugacy/Conjugacy.jl	61.00% <100.00%> (+0.18%)	⬆️
src/NumFieldOrd/NfOrd/MaxOrd/MaxOrd.jl	73.98% <0.00%> (-5.04%)	⬇️
src/Map/NfRelOrd.jl	88.29% <0.00%> (-2.13%)	⬇️
src/NumFieldOrd/NfOrd/Ideal/Ideal.jl	77.36% <0.00%> (-1.70%)	⬇️
src/NumFieldOrd/NfOrd/Unit/FindUnits.jl	76.85% <0.00%> (-1.39%)	⬇️
src/NumField/NfAbs/CompactRepresentation.jl	82.16% <0.00%> (-0.96%)	⬇️
... and 26 more

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