Another media player intents potential fix

[timusus]

Fixes #106

This change adds the necessary intent filters and handling code to allow Shuttle2 to be recognized by Android as a music player application.

Changes:

• Add MUSIC_PLAYER action to register as a music player
• Add ACTION_VIEW intent filters for audio file types (audio/*, application/ogg, application/x-ogg, application/itunes)
• Update MainActivity to handle ACTION_VIEW intents for audio files
• Update PlaybackService to process ACTION_VIEW intents via media session

This allows users to:

• Set Shuttle2 as the default music player
• Open audio files from file managers and other apps with Shuttle2
• Have Shuttle2 recognized by other apps that integrate with music players

[rivaldi8]

This allows users to:

• Set Shuttle2 as the default music player
• Open audio files from file managers and other apps with Shuttle2
• Have Shuttle2 recognized by other apps that integrate with music players

I haven't found any option in my phone or the emulator to set the default music player, and I'm not sure what the third item refers to. However, I've tested opening files from a file manager and it doesn't work as it is.

There are some things missing that I needed to add for it to work properly. You can find the changes in the branch alexm-106-open-audio-files-intent (rebased to main), if you want to cherry-pick them. Or I can open a separate pull request, if you prefer.