Reading and writing of schedule JSON representation to harddisk

The internal representation of the Schedule has been designed around a JSON data structure. This means that it should be possible (in principle) to store this to disk and recover the Schedule at a later point in time.

For the Pulsar_QCM backend, we require storing JSON files with assembly and waveforms to disk. It makes sense to also store the Schedule JSON next to it as this contains information relevant for visualization and simulation and is in general more readable.

TODO

• Add string representation to Gates
• Add string representation to Pulses
• Add string representation to Resources
• Add string representation to Acquisition Protocols
• Add unit tests for serialization.
• Add unit tests for deserialization.
• Verify Schedule that the schedule is valid json
• [Refactor] Change key 'operation_hash' to 'operation_repr'