Log Message:
schismtracker: Update to 20200412

Summary of changes since 20190805 release:

    Fix problem with switching tabs on the Instrument List page using the \ 
keyboard, introduced in 20190722 release.
    Implement incremental search on Load Instrument page, like on the Load \ 
Sample and Load Module pages.
    Correctly display size of exported mono files before exporting.
    Add "AudioVideo" category to Linux desktop entry.