Trace input handling

Additional docu and first tests

See merge request !2

Trace input handling

Rest Gateway is used for HTTP POSTing new trace - sends message with trace to Trace Retrieval - TR saves trace in MongoDb and informs Semantic Linking - SL loads all traces via HTTP Get from TR and calls processing method.

See merge request !1

Fixed workaround from commit bf2c831c. 
Traces are loaded via REST Get instead of direct DB access.

Fixed workaround from commits d6ec9dd5 and ee789e29.
Messages are now sent asynchronously and connection is reused with multiple channels

Pika BlockingConnection in MessageSender somehow doesn't send heartbeats to RabbitMQ correctly. Opening new connection for each message now

Fixed trace forwarding to Trace Retrieval; disabled message receiver

Working message sending and receiving while running the flask service