Several sude/*.json schedules can exist on disk; only one runs at a
time, chosen by a client Load. Sud no longer takes a path at all - it
starts empty (EMPTY_SUD) and the server config no longer names a
specific schedule file, removing the implicit link to sud_0010.json
in particular. Reading/writing sude/*.json is now entirely the
client's job (e.g. the GUI's Load/Save file dialogs); the server's Sud
only ever holds whatever was last Load()ed, in memory, until replaced
or the server restarts.
Updates demo_sud.py/demo_sud_save_load.py to construct an empty Sud()
and load() a schedule explicitly, matching the new constructor.
Renames everywhere the concept appears: Sud.download()/upload() ->
save()/load(), the 'Download'/'Upload' websocket messages ->
'Save'/'Load', the brewpi_gui menu actions, handlers and
sud_download_path -> sud_save_path, and the demo script. Behavior is
unchanged - this is naming only, from the client's perspective (save
to / load from a local file) rather than the server's.
jens