Implement CUDA BwdTrans sum-factorization kernels

See merge request !11

Add a `Field::compare` method

See merge request !9

Add IProductWRTBase operator and standard matrix implementation

See merge request !10

Fix/wrong expid for block

See merge request !5

Add unit test for BwdTrans operator

See merge request !4

remove unnecessary std::move from Operator ctors

See merge request !6

fix Field move assignment ctor

See merge request !7

Implements BwdTrans StdMat operator

See merge request !2

Updated code to use a common base class and single factory pattern.

See merge request !1

Expand on the comments in main.cpp.

Explicit instantiation of OperatorFactory with doubles.

Tried to move boilerplate code up to base class.
Added operator type descriptor/trait structs.
Replaced enums with typenames.

Still has multiple definition linking errors to fix.