Centralize Language Settings

[pbui]

Right now the programming language information is spread out across multiple files:

• scripts/run.py: Specification of how to execute code for that language
• dredd/handler.py: Listing which languages are supported
• Dockerfile: List package to install
• tests/test_code_echo.sh: Echo test code

I would like to have a single YAML file for configuring the programming languages and then either generate those parts of the system or to have those parts read the configuration file at run-time. This will make it easier to add new languages and to ensure everything is working correctly.