Spirc: Replace Mecury with Dealer

[photovoltex]

As suggested from @roderickvd a draft PR so i can have some community feedback and give now and then updates on the progress.

The replacement is in a working state, so the very basic do work again. There is still a lot of cleanup and re-implementing to do.

But so far what is working:

• transferring the playback so that we are the player
  • funnily enough, transferring back isn't working yet
• play, pause, resume, prev, next, seek
• just general communication of our state to other clients

Known Problems:

• on the initial connection librespot doesn't appear, but if for example the volume is slightly updated, we should appear
• if the session or spirc/dealer dies, we lose our complete ConnectState
  • it would be nice if that is preserved so we could start from that again
• sometimes other client's forget that we are the current player
  • might be that that is already resolved, but i think i still saw that behavior not so long ago

What i still have to do:

• handling the remaining request commands
• transferring the state to a different player again
• resolving the context from a cold state
  • currently it works really well if the playback starts from a different device like the web-player,
  • but from a cold start it's still a bit weird and not fully sorted out
• shuffling has to be re-implemented
  • we can set restrictions for the clients getting our state
  • so for autoplay we should ignore shuffeling and just disable repeat and shuffle
• i added the option for track repeat, but it's not handled yet
• i would like to remove the remaining mercury calls
  • but for that i will have to see if the dealer sendes equivalent messages/requests

I tried to keep my code clean, but if there are points that i could improve and such, i would like to here them^^

[photovoltex]

oh the branch might not compile because there are still some todo!() here and there which result in unreachable statements that clippy, understandably, doesn't like.