Support more static arrays

[daanhb]

Right now, a "Euclidean domain" is defined to be:

const EuclideanDomain{N,T} = Domain{SVector{N,T}}

It may be more generic to make this into:

const EuclideanDomain{N,T} = Domain{<:StaticVector{N,T}}

That would support other kinds of static vectors apart from SVector.

[dlfivefifty]

Actually maybe not: Domain{<:SphericalCoordinate} is definitely not Euclidean

[daanhb]

Fair point!

[daanhb]

Alright let's leave this potential change until it is genuinely needed somewhere else, and then figure out a clean solution.