[Analytics] ShareVR Unity Log System

[chenchen2015]

Description Create log system infrastructure in ShareVR Unity SDK to log user behavior and session information. This will be connected to #42.

[chenchen2015]

Primitive metadata log system ready and tested in SDK v0.4

New TODO:

• [ ] Implement log to temp file method in Unity
• [ ] Test the reliability of log file creation and S3 upload