Publish reframed Annotations on Current Step

[Archdoog]

• Removes hard coded annotation type in favor of BTreeMap for annotations. This gives us the flexibility of any json attribute an API wants to return plus keeps the json keys sorted for consistency and testability (since we're passing this as a json string through the FFI)
• Reshapes the original annotations format of many arrays of a single value into one array with an object of key value pairs (making it easy to pass to a client platform).

Closes #89

Two follow up tickets are:

1. Parsing the data on the client side is here: Convert AnnotationValue to parsed type instead of Map in Android & iOS #271.
2. Convert MaxSpeed to something reasonable: Convert MaxSpeed to consistent JSON format (a float of meters per second) #272

[ianthetechie]

Here's a first pass over it. Honestly I think this is fine methodology-wise. We can debug the indexing issues tomorrow, but I think the approach is probably fine so you can proceed with refinements and clean-up.

[ianthetechie]

Few more comments... We're really close on this :D