Adds a 'System' channel for static, global info that doesn't belong
to any one task - sent once at startup directly from brewpi.py's
__main__ (a client connecting later still gets it via the
dispatcher's global_state replay on subscribe, same mechanism
SudTask's startup Name/Description already relies on).
Moves warp_factor out of SudTask's startup message and into this new
channel, since it's not actually Sud-specific - it's now available
(and the status bar shows it) even without a Sud configured. The
forecast plot's progress-line scaling switches to the same general
Window.warp_factor field.
Displayed via a permanent status bar widget (not cleared by the
existing transient step/schedule showMessage() calls).
jens
56de5cf4d6