Update the Download section of the docs.

[luongvm]

Problems:
In this page http://samsungxr.com/downloads/ user still pointed to use the org.gearvrf sdk. I think this should be eventually updated to the new sdk under the class com.samsungxr but I went to check by google there's no such sdk uploaded.

A cross check found this unresolved ticket waiting from 6 days ago https://issues.sonatype.org/browse/OSSRH-43936

The verification TXT for this ticket is in place, so I guess there's no more blocking issue on SS end to push this repo to the public.

Solutions:

1. Resolve the ticket to create maven repo.
2. Update the Download section to the correct package.
3. Update the SXRApplication template (linked with The instruction to getting started a new Android project is not working #11 ), which should be in a separate issue and PR in the sxrsdk-demos.

[liaxim]

1. is done
2. documentation repo has been updated, site update pending
3. template has been updated; uses snapshots now