In theory different UIs can show different meter-types, so it
can make sense to maintain the type in different places.
MeterType is a bit-set and PeakMeter implementation provides for this.
However, this is not being used, and the current implementation
was rather fragmented, cross-connected signals to keep types in sync,
allowed inconsistent meter-types in GUI and backend.
MeterType is now kept by meter itself, however it is still
saved/restored as part of the Route state.
N.B. This change breaks the API, various methods have been renamed
for consistency.
cd5b0819bf