Update and refactor the repository

[RichardKlem]

Hi, I was experimenting with this repository and I updated and refactored the repository along the way.

Changes done:

• Convert from Java to Kotlin (preferred language for Android, only syntax, no extra changes in functionality).
• Versions of gradle and other libs and tools bump.
• Deprecated configs are updated.
• Removed the local.properties file.
• Add launcher icons.
• Correct README.md .gif links.

I tested singlepose and multipose apps with all models on both front and back cameras. I believe keeping it up to date helps others when experimenting with this repository. :)