multi-device support

This PR adds support for sending to and receiving from multiple ThingsBoard devices (issue #2) as well as general code refactoring and a few additional features:

• refactored into thoscy modules: TBSender, TBReceiver, oscparser, jsonparser
• added support for multiple devices (receiver currently has bug)
• added support for json config file
• added support for receiver login credentials via env variables: THOSCY_USER and THOSCY_PASS
• fixed string parsing in wrapper scripts
• removed unused python lib requirements
• some README updates (though not finished)

When finished, this work will likely become Thoscy version 1.0.0.

TODO

• fix receiving bug where it's not currently possible to tell which device is sending a telemetry update (see companion issue opened on the ThingsBoard Github repo)
• update README with new features
• add multi send and receive examples as well as sample config.json file
• additional testing