Replace initializetomography with more specific names

[mtfishman]

Proposal to replace initializetomography with more specific functions randomstate and randomprocess. The interface could be something like:

• randomstate(MPS, N) # Make a random qubit wavefunction for pure state tomography
• randomstate(LPDO, N) # Make a random mixed state as an LPDO
• randomstate(MPO, N) # Make a random mixed state as an MPO
• randomprocess(MPO, N) # Make a random unitary circuit as an MPO
• randomprocess(Choi, N) # Make a random Choi matrix, defaults to Choi{LPDO}
• randomprocess(Choi{MPO}, N) # Make a random Choi matrix in MPO form

Additionally, these options could be chosen with flags, like:

• randomstate(N) = randomstate(MPS, N)
• randomstate(N; mixed = true) = randomstate(LPDO, N)
• randomstate(N; mixed = true, lpdo = false) = randomstate(MPO, N)
• randomprocess(N) = randomprocess(MPO, N)
• randomprocess(N; mixed = true) = randomprocess(Choi{LPDO}, N)
• randomprocess(N; mixed = true, lpdo = false) = randomprocess(Choi{MPO}, N)

Here I'm assuming lpdo = true is the default, since it is probably most common, but could be chosen the other way.