Option to set credentials for the HTTP server

[klehmann]

It looks like ti_touchdb does not yet support setting credentials for the embedded HTTP server that provides CouchDB REST APIs.
Would be great if this could be added in ComObscureTiTouchDBModule.m.

AFAIK Couchbase lite on iOS provides support for multiple credentials, while Couchbase lite on Android only seems to support one pair as of V1.0.

For our application we would need to have multiple credential support and it would be great to be able to change them while the app is running.