Default device does not respect device-specific control method

[d-uzlov]

Expected behavior

I set linear control method for device X and logarithmic method for device Y.
I select Windows Default as a primary device to control volume.

I expect that app will automatically switch to appropriate control method, depending on which device is currently set as default.

Actual behavior

Windows Default is like a separate device, for which you have to choose one control method.
Per-device settings are ignored when Windows Default is selected.

If I select some device and then switch to Windows Default, settings UI automatically sets control method to match previously selected device but it's just settings UI, you still have to manually save it.

Desktop:

• Windows version: 10 20H2 (19042.928)
• Volume² version: 1.1.8.457

[d-uzlov]

I think that following UI changes will make per-device control easier to use:

• Control method drop-down list should be disabled when Windows default entry is selected
• There should be a second drop-down list: Default control method
• Control method for specific devices should contain a new 4th entry: Default
• In the device list icons with curve should be displayed for all devices where non-Default control method is selected