Add Bigscreen plugin with support for Bigscreen STT packet type

Summary

Feature adds a new plugin for Plasma Bigscreen to support the android bigscreen plugin, the plugin handles receiving the Bigscreen STT type network packet and emits the contents of the packets to a qml interface on Plasma Bigscreen.

Test Plan

Create a connection to bigscreen interface in QML and listen for onMessageReceived signal which emits the message contents of the Bigscreen STT packet, it can then be used to forward it to any natural language intent based application or service, in the case of Plasma Bigscreen the transcribed STT contents are sent to Mycroft for voice actions.