Refactoring of PycQED test suite

[MiguelSMoreira]

After consultation with the current users of PycQED, the importance of each of the tests in PycQED was assessed. These were categorized into 3 classes: important, non-important, and to-be-removed.

The first class encompasses all the tests that must be actively maintained, the second all the tests that will be kept but whose removal may be determined at a later date. Finally, all the tests in the third class will be removed as soon as possible. Following is the complete list of all test currently in PycQED, divided into the aforementioned categories:

Important tests:
test_MeasurementControl
test_SSRO_analysis
test_cliffords
test_detectors
test_flux_formula
test_gst
test_hdf5_datasaving_loading
test_heterodyne_analysis
test_kernel_distortions_ZI
test_lfilt_kernel_object
test_pauli_transfer_matrices
test_pq_parameters
test_pygsti_helpers
test_qubitspec_analysis
test_spectroscopy_analysis
test_timedomain_analysis
test_utilities_general
test_waveforms
test_waveforms_flux
test_analysis_toolbox
test_basics
test_data_manipulation
test_VNA_complex_reso_analysis
test_base_analysis_v2
test_coherence_analysis
test_cryoscope_analysis
test_dac_scan_analysis
test_gate_set_tomography_analysis
test_randomized_benchmarking_analysis
test_simple_analysis
test_timedomain_analysis_v2
test_device_objects
test_qubit_objects
test_flux_lutman
test_mw_lutman
test_ro_lutman
test_UHFQC
test_ZI_HDAWG8
test_CC
test_QWG
test_clifford_rb_oql
test_multi_qubit_oql
test_openql_helpers
test_pygsti_oql
test_single_qubit_oql

Non-important:
test_amsterdam_waveforms
test_butterfly_analysis
test_chevron_sim
test_kernel_distortions
test_misc
test_multiple_AWGs
test_pulsar_element
test_pulse_scheme_drawer
test_qasm_compiler_XFU
test_qasm_instruction_lib
test_qasm_loader
test_qasm_to_asm
test_qumis_assembler
test_single_qubit_tek_seqs
test_tomo_v2
test_tools_plotting
test_Two_state_T1_analysis
test_alignment_analysis
test_readout_analysis
test_syndrome_analysis
test_timing_cal_analysis
test_mock_CCL_transmon
test_generate_CCL_cfg

To be removed:
test_tomo
test_tfd_analysis
test_distorter

[wvlothuizen]

great idea, maybe this is also a good place to bring my old PR to attention (#620), which moves old cruft out of the way