Support remote Json Serialization in runOnInstance

[lbwexler]

Support remote Json Serialization in runOnInstance

• Also hardened Exception transport back to calling server generally. Had seen some exceptions failing to serialize in the past, and general theme here is to avoid serializing unknown things we don't need to.
• Also added a fix to File Downloading, which was failing to serialize files on my local machine -- now simpler, just passes the bytes.

Great improvement suggested by Jakub -- could become especially useful for any application than needs to run various things on the primary server. The return objects no longer need to be serializable!