Add command line tool to install scaffold.

[tompollard]

This pull request adds a command line tool called startproject:

omopetl startproject <PROJECTNAME>

Running the command installs the following scaffold files at <PROJECTNAME>:

templates
├── README.md
├── data
├── etl_config.yaml
├── mappings.yaml
├── requirements.txt
├── scripts
│   ├── extract.py
│   ├── load.py
│   └── transform.py
├── tests
│   ├── test_extract.py
│   ├── test_load.py
│   └── test_transform.py
└── validation.yaml