Better startup/runtime device addition/removal handling

[megabug]

• Device scanning should happen in Application creation
• Device scanning, connection and disconnection should be in background thread (if it isn't already?)
• Remove metadata from manifest so app stays up when device connected
• Show toast on device connection/disconnection
• Standardise language (connect/attach, disconnect/detach, etc.)

[megabug]

• Device scanning should happen in Application creation: done in 5998d1d9ab2c9f59da206f8a7dc1a53563755852
• Device scanning, connection and disconnection should be in background thread (if it isn't already?): done in 8d97554a121e5fe0b5d47f07a778f477731b66b9
• Remove metadata from manifest so app stays up when device connected: done in 61c3b22ebf0a646fc32bc84e540aebf7c58a1f2c
• Show toast on device connection/disconnection: done in 6a29ffad58d6e7a2c7e60b27c2339fa5b17659e0, 70eb100a64e6501ebdfaa26480c5811e5e564a37
• Standardise language (connect/attach, disconnect/detach, etc.): it's ok (connect/disconnect)