Small fixes on handling the archives of DeviceStorage :
- hide the keyboard before displaying a warning on 'small' archive
- Keep the trailing slash in archive directories
- If the last selected archive does not exist any more in Device Storage, do not attempt to set it in the drop down list
- Putting the archive files at the root of the sdcard seems to cause issues (high CPU usage on the Simulator) : if it is the case, give a warning to the user and do not use this archive