LV2_PATH is set in a wrapper script because variable substitution
doesn't work.
VST_PATH doesn't need to be set we patched the default location in
the source. See #139
patches/audacity-suil-fix.patch is necessary for suil (LV2 UI) to
work. A fix was submitted upstream in the past but was ignored.
This version of the patch is highly specific to flatpak.
screenshots: before 3.4, Audacity pulled the rug by removing the
screenshot, and removing them from the appstream file. This is the
path of least resistance.