Add equalizer presets to library to simplify implementation in Home Assistant

[Solmath]

As pointed out during review of home-assistant/core#162956, the presets should be part of the library.

This PR adds presets, as well as class methods to simplify implementation on HA side.

Note

I noticed that

eq_settings = UserEQ.from_preset("bass_boost", enabled=True)
await client.set_equalizer_params(eq_settings)

will currently not actually enable the equalizer.

The reason is that the payload in set_equalizer_params() only contains user_eq_bands but not user_eq like in set_equalizer_mode().

Should we change that, so the EQ will automatically be activated when selecting a preset?

To change presets in the StreamMagic App, you have to manually activate the EQ first.