Mqt.ddsim

* new `hybrid_qasm_simulator` and `hybrid_statevector_simulator` backends for Qiskit that expose the hybrid Schrödinger-Feynman decision diagram-based simulator proposed in https://arxiv.org/abs/2105.07045
* new `unitary_simulator` backend for Qiskit that exposes the efficient decision diagram-based methods for constructing functional representations of quantum algorithms proposed in https://arxiv.org/abs/2103.08281

* Import assembled QasmQobjExperiment instead of QuantumCircuit (via QFR, thanks burgholzer )
* Add unit tests to test python code
* Add jkq/* folder to clang-format checks
* Updated README.md
* Unified workflow for bindings (one workflow with conditional job to publish to PyPI)
* StatevectorSimulator now inherits from QasmSimulator and only sets some class variables (inpired by Qiskit's BasicAer)
* Properly handle barriers in CircuitSimulator (i.e., ignore them)

Update submodules to use the new _sorted buckets_ feature in the DD_Package which increases the performance, especially for more complex circuits.

This release adds capabilities for hybrid Schrödinger-Feynman simulation using decision diagrams based on the ideas outlined in:

[[1]](https://arxiv.org/abs/2105.07045) L. Burgholzer, H. Bauer, and R. Wille. **"Hybrid Schrödinger-Feynman Simulation of Quantum Circuits With Decision Diagrams"**. [arXiv:2105.07045](https://arxiv.org/abs/2105.07045), 2021

In order to use the new simulator, call the `ddsim_simple` executable as follows
bash
ddsim_simple --simulate_file_hybrid <FILE> --hybrid_mode amplitude --nthreads 4 --ps

where
- `<FILE>` specifies the circuit file to be simulated (the format is derived from the extension)
- `--hybrid_mode` specifies the mode to use, either `amplitude` (*default*) or `dd`
- `--nthreads` specifies the number of threads to use for the parallel simulation

Python bindings for DDSIM and Provider/Backends for Qiskit

- Python bindings for standalone usage
- Provider and Backends for Qiskit
- QasmSimulator for sampling
- Statevectorsimulator to get the state vector
- and more to follow :)

* Noisy+Approximating Simulation with new Package
* Refactor Noisy Simulation code
* Noise for multi target gates
* Use exceptions instead of std::exit
* Nicer JSON output with nlohmann lib
* More informatative exceptions
* Format fixes
* Ignore parts of file for format
* Added tests
* Updated README
* Updated LICENSE