Improved README.md and GitHub templates

Added

• Shield repository file
• Copier will ask branch name for git init (defaults to main)
• GitHub template for bug report, feature request and pull request (using Facebook Reasearch' Hydra project's templates)
• CONTRIBUTING.md file (Also based on Hydra, but significantly simplified)

Changed

• README.md scaffold.
• File name captalizations (LICENSE.txt, README.md)

Removed

• Unused copier.yaml versions