Repair debug entry point after using absolute imports

Using absolute imports broke the debug target due to
a Werkzeug bug:
https://github.com/pallets/werkzeug/issues/461
Solution is to avoid running Flask apps using
"python -m", and to use "flask run". This also
gets rid of the coverage exception for
"__main__.py".

.coveragerc

@@ -1,3 +0,0 @@
-[run]
-omit =
-  stw_potsdam/__main__.py

Makefile

@@ -1,5 +1,5 @@
 
-RUN = pipenv run python -m stw_potsdam
+RUN=FLASK_APP="stw_potsdam.views" pipenv run flask run
 
 dependencies:
 	pipenv sync --dev

stw_potsdam/__main__.py

@@ -1,4 +0,0 @@
-# -*- encoding: utf-8 -*-
-from views import app
-
-app.run()