Batogram

Various usability improvements:
* The mouse wheel can now be used together with shift or ctrl to zoom just the time or frequency
range, leaving the other axis range unchanged.
* A new file menu item "close all" closes the folder browser and any spectrograms currently open.
This is useful if data files are being read from mountable media such as an SD card.
* Added a settings button in the folder browser allows the visibility of additional columns to be controlled.
* The "send item to trash" option in the flagged item modal is no longer initially selected, to avoid accidents.
* Added grid lines to the amplitude graph so that timings can be more easily read from it.
* Added a refresh button to the spectrogram panels to reload/reload data from file - useful
if the file is updated.
* Updated dependency modules to recent versions, and made requirements.txt a little more forgiving about using
compatible versions.

* Fix to make flagged folder item actions compatible with Windows file system semantics.

* Major improvements to the folder browser to support flagging of items.
* Improvements to the actions modal which is now more logic and allows copying of items.

* Added the ability to open a folder of audio files and conveniently cycle through them.
* Added a setting to override the sample rate inferred from the wav file, which may not be correct in rare cases.

* Added audio playback.
* Added support for frame data and direction-based colour rendering (specific to the BatGizmo microphone).

* Added multichannel options.
* Added support for reassignment spectrograms for increased resolution.
* Added support for window padding for increase frequency resolution.
* Made guano parsing more tolerant of unexpected data and types.
* Fixed a regression so that the sampling rate in the guano metadata overrides the one in the .wav file header.