They is really no needed with the new _get() API and the WpSpaJson API. In C,
users can use 'wp_spa_json_parse_{boolean|int|float|string}()' APIs to parse the
WpSpaJson. In Lua, users can just do 'Settings.get(setting, m):parse()'.
If a route specifies a set of profiles, it should not be used if the
profile is not in that list.
In findBest/SavedRoute, exclude routes that don't match the active
profile.
Currently in the SPA devices, the device id is different for different
profiles so this condition does not occur, but in general this might not
be so.
It's safer to have the default volume value at significant attenuation,
to mitigate situations where the output is at high gain.
Use linear scale 0.4^3 (-24 dB), which puts Pulseaudio volume sliders at
40%, as a better starting value than 0.4 (-8 dB / 74%). E.g. for many
Bluetooth headphones, the volume at 74% is still uncomfortably high, and
a lower value is better.
This makes the configuration more consistent. The storing of the default routes
logic needs to be implemented eventually in a C module-default-routes, similar
to module-default-profile.
