make RotationBlock composite block

[Roger-luo]

It looks strange that:

julia> rot(chain(X, X), 0.1)
rot(nqubits: 1, datatype: Complex{Float64}
chain
├─ X gate
└─ X gate, 0.1)

it would be much better if it is just a container

julia> rot(chain(X, X), 0.1)
nqubits: 1, datatype: Complex{Float64}
rot(0.1)
└─ chain
          ├─ X gate
         └─ X gate, 0.1

since composite should simply means the composition of other blocks.

[GiggleLiu]

Agree, but let’s make it slow. It is still confusing that whether a generator should be regarded as a gate or not. Let’s see more feedbacks.