Correct similarity transforms of operators

[jagot]

The operators returned by get_operator are usually wrapped as R*M*R' which is fine if R'R=I, but this is generally not the case. Instead, the expression should be R*M*inv(R), which is dependent on ContinuumArrays.jl implementing inv(::AbstractQuasiMatrix) and that inv(R)*R=I is a no-op.