Improve context getting

[mwvaughn]

Almost all SD2E actors have the following boilerplate code in their reactor.py

    mes = AttrDict(rx.context.message_dict)
    if mes == {}:
        try:
            jsonmsg = json.loads(rx.context.raw_message)
            mes = jsonmsg
        except Exception:
            pass

The rationale for this is that agavepy.actors#get_context fails to deserialize some JSON messages due to valid characters in the message that cannot be parsed by ast.literal_eval(text) (see https://github.com/TACC/agavepy/blob/master/agavepy/actors.py#L65)

[mwvaughn]

After conferring with @joestubbs we will improve agavepy.actors#get_context rather than bolting this behavior on to the SDK.