Adds File menu actions to save the running Sud's schedule to a local
sud.json and to replace it from one, via the Sud websocket channel's
new Download/Upload messages. File dialogs are opened up front on the
GUI thread; the actual read/write happens off the websocket recv
callback, which runs on a worker thread and must not touch Qt itself.
main_window.py is regenerated from brewpi.ui via pyuic5 5.15.11, which
also picks up an unrelated pre-existing drift (the default URI had
fallen out of sync with the .ui source).
jens
bb94e065f4