Clean up repo and spin various files out into folders/other projects

[vnegnev]

• spin out examples.py into a separate folder; write standard example functions
• move test_rx_scaling() and test_gpa_calibration() from experiment.py into a tests folder or separate file (figure out later)
• implement shimming and delay compensation in the grad_board classes
• rewrite README
• ref_loopback.npz: check what uses it [aim to have a built-in hardware loopback test]
• test_flocra.py: rewrite to be called test_flocra_low_level.py
• redo test_gpa_fhdo.py/seq to test_grad_board.py
• move other tests (e.g. test_server) into a separate folder
• rip off flocra-pulseq's compression for complex TX data, or replace slightly