In
b53a034aaf (diff-0339cf92cc68bc5981fe6df601316c1c)
I removed this, because RN has updated the builtin JSC version. On the next
release, however, RN introduced a new JS interpreter (Hermes) so JSC is now a RN
dependency. Thus, add the magic spells to publish the AARs to Maven.

People run these in their own checkout and will run into problems because
tagging will fail.

- don't hardcode defaults in gradle files
- allow for uploading also to HTTP URLs
- support HTTP authentication when publishing

It releases the SDK and all dependencies (including React Native) to the
specified Maven repo.