strip/bus levels compared by index iteratively.
strip/bus level array size added to _base_vals dataclass. Helps to keep track of level array size when switching between kinds.
level_offset class attributes added to strip/bus/gainlayer labelframe classes.
watch_levels adjusted to only updated frames when a level has changed.
ldirty added, true iff level value has changed.
fetching level arrays moved to highest level of the app.
pdelay and ldelay added to _base_vals dataclass.
