[Refactoring, DA] More flexible analog blocks implementation

[madagra]

Increase flexibility of how the AnalogBlocks are defined.

Close #108

[jpmoutinho]

The goal here is to have a flexible way for the user to specify how a given RX/RY/RZ angle is converted into the drive Hamiltonian, instead of using the currently hardcoded omega = pi.

When fixing it we also need to take into account the pulser backend config, currently using the params amplitude_local, amplitude_global and detuning to go around this in pulses.py.

Fixing this will also close #108.