Add .dockerignore file for Docker build

This significantly reduces the build context from:

```
Sending build context to Docker daemon    916MB
```

to:

```
Sending build context to Docker daemon  3.713MB
```

.dockerignore

@@ -0,0 +1,19 @@
+.git*
+__pycache__
+*.pyc
+*.pyo
+*.pyd
+.Python
+.tox
+.venv
+.coverage
+.coverage.*
+.cache
+.mypy_cache
+.pytest_cache
+docs
+test
+static
+vagrant
+LICENSE
+report.json