Automated QA checks for preprocessing

[celefthe]

Add automatic QA checks to preprocessing, so that poor quality recordings or preprocessing failures can be flagged efficiently during batch runs.

Add these to qa modules as check_ functions. These should be reported in the print logs, stored in the resulting HDF5 files and there should be a separate check command to interrogate HDF5 files to see if the data contained passes QA. These checks should also be included in the associated HTML reports.

For preprocessing, the following should be included:

• Channel histogram separation (also in Channel separation to autodetect histogram separation failure #29)
• Timestamp drift check - i.e. is the recording "jumping" beyond an acceptable range (two standard deviations).
• Noise levels (see CASCADE for calculation)
• Signal-to-noise ratio (maybe - SNR map in report..?)
• Bleaching detection - signal drift (do peaks get lower?)

For registration:
- [ ] #81

[celefthe]

Split auto QA for registration in separate issue

[celefthe]

Leaving check command for separate issue (#85)

[celefthe]

Closed in #86