Pare down files copied into container by Dockerfile

Copy in the minimum necessary files for a successful install and run to cut
down on caching forcing changes to the container. This will cut down on
unnecessary docker build cache misses when using the run script.

Author: mcdonnnj

Dockerfile

@@ -8,7 +8,15 @@ COPY requirements.txt .
 
 RUN pip install --no-cache-dir --requirement requirements.txt
 
-COPY . .
+COPY scripts/ scripts/
+
+COPY trustymail/ trustymail/
+
+COPY README.md .
+
+COPY requirements-dev.txt .
+
+COPY setup.py .
 
 RUN pip install --editable .