RGBD odometry: separate rgb_transport and depth_transport params

[rayferric]

Currently, there's just a single image transport parameter, which practically cannot be set to anything other than raw, since depth cannot be transported using compressed and color can't use compressedDepth either.

This PR separates the image_transport parameter into two, rgb_transport and depth_transport, which will allow for compressed input.

Note: There's also an unrelated change that introduces the call to resolve_topic_or_service_name prior to subscribing, which helped with subscribing to remapped topics in a namespace IIRC.