Externalize file database backup.

Move the import/export file database from WineDB into
FileDatabaseBackup.
Update guava version
Provide Google Play install link in README.
Remove icon from ActionBar.
Fix bug: scanning crashes due to progress dialog.
Fix "Wine modified?" bug.

Now the SingleWineView will ask you "Save before quitting?" when you've
modified an existing Wine, if you've created a new Wine with some
values, or if you've scanned a new Wine and it has populated fields.