org.subsurface package changed to org.ssrf

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.ssrf (short form of subsurface)

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