Add support for phase, sqrt(X), and delay gates to simulators

[chriseclectic]

Summary

• Adds support for parameterized delay gate to all simulators and methods. This is treated as an identity.
• Adds support for parameterized phase gate "p" and controlled-phase
  gate "cp" to the statevector, density_matrix, unitary, and superoperator simulators. These are identical to u1 and cu1 gates.
• Adds support for multi-controlled phase gate "mcphase" to the statevector and unitary simulators. This is the same as an mcu1 gate.
• Adds support for the sqrt(X) gate to the statevector, density_matrix, unitary, and superoperator simulators
• Deprecates the x90 decomposition of the NoiseModel class. This functionality can now be handled by transpiling to sx or rx plus one of p, u1, rz basis gates.

Details and comments

[vvilpas]

LGTM!