Use new Implementation ID server URL, and support redirects and https in our custom HttpClient class

Background and Scope

We have a custom implementation of org.openmrs.util.HttpClient, which I believe is only used in openmrs-core to post data to the Implementation Id server.

In the long run we should remove this class, and there's another ticket for this: TRUNK-5366.

In the short run, our HttpClient code does not support redirects, and may not support https (TRUNK-5372). Because of some changes to our infrastructure (see here) we need to support redirects, so this ticket is to do a quick-fix, and backport it far (maybe even to unsupported OpenMRS versions).

Acceptance Criteria

1. The URL that we hit for our Implementation ID server should be https://implementation.openmrs.org/
2. Our code should transparently handle the fact that this might redirect somewhere

Dev Notes

Relevant code is at https://github.com/openmrs/openmrs-core/blob/2.1.2/api/src/main/java/org/openmrs/util/HttpClient.java

We should backport this fix as far as 1.9.x (normally we don't do this, but it's needed in this case to help someone test out the Sync 2 module, which is a community priority of ours).