applet/main: Add change sink/source with global shortcuts and mic osd

Adds the ability to change default source/sink by shortcut, along with osd for mic change.

Default Keybinds are set to:

• Mic Controls bound to Meta + Volume Controls
  • Mic Mute : Meta + Mute
  • Mic Volume down : Meta + Volume Down
  • Mic Volume up : Meta + Volume Up
• Sink Controls bound to Control + Volume up/down
  • Next Sink : Control + Volume Down
  • Prev Sink : Control + Volume Up
• Source Controls bound to Control + Volume up/down
  • Next Source : Alt + Volume Down
  • Prev Source : Alt + Volume Up