API to load and send .rbl file from code

[jleibs]

To work around situations where blueprint APIs don't yet cover features, users can still manually edit blueprint in the viewer and save them. Unfortunately these blueprints still need to be distributed and manually loaded.

We should add a logging API that opens and existing .rbl file, and sends it to the viewer.

for example:

blueprint = rrb.Blueprint.from_file("my_blueprint.rbl")
rr.send_blueprint(blueprint)