Added the Speech Module

[KritiaSthovania]

Added the Speech Module as well as third-parties resources. I deleted those for other platforms, e.g. IOS and macOS. For the SpeechSDK and the Vosk models which cannot be packed in the unity package, maybe we can pack them in the Release as separated files.

Update: The above-mentioned problem is solved. The third-party files are here: https://github.com/rwth-acis/i5-Toolkit-for-Unity-SpeechModulePlugin

Since the return value of Login() method was changed, I also fixed a bug in the RocketChatClient sample scene.