Moved export error handling to the export method itself
Redesigned handling of internal/external paths to deal with various file and SD card issues

Also increased version number to 18 to handle change in directories
Fixed an unclosed stream in BluetoothObserver
Removed unnecessary string format (potential locale issues)

Also removed unused string from strings.xml
Use inbuilt getString to format string arguments (rather than String.format)

Also added a plural for narrative deletion confirmation
Show the notification bar on touch during playback - fixes UI issue before first playback bar hide