swmr implementation

[Harrison-Oatman]

Implemented swmr mode for data saving. Major changes

• hdf5 mode is now the only mode for saving data. This is basically how it already was, because tifs are not well supported here.
• hdf5 files are opened at the beginning of the experiment, and kept open until the experiment closes / fails
• hdf5 files are saved by MicroscopeOutbox in swmr mode, which allows other processes to open the files during the experiment
• convert_hdf5s.py opens files to read in swmr mode, which should not interrupt the ongoing experiment.
• AquisitionEvent class no longer keeps a "super_axes" parameter, which had been kept around in case we wanted to organize hdf5 files into different folders. I don't see a good use case for it, and it makes the implementation of microscopeoutbox more confusing, so I've removed it.