org.subsurface package changed to org.subsurface.downloader

Fixes #9

org.subsurface is also the package name of the subsurface companion application.
And when these two applications are installed on the same device, android always
thinks of this application as the downgraded version of subsurface companion.
Hence changed the namespace to org.subsurface.downloader

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Added default save location preference.

Fixes #6

Default file save location of imported dive xml and logs. This path is appended
to default external storage.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>
Close UsbDevice on finish

After finishing import, finish the USB device.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>