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