Always give absolute template_folder and static_folder to Flask

For some reason, `pkg_resources.resource_filename` returns a relative path
if we call Mutalyzer using `python -m mutalyzer.entrypoints.*`. The path
is of course valid, but we pass it to Flask, which assumes relative paths
to be relative to the Python package root. To circumvent this incorrect
assumption, we first make the path absolute before passing it to Flask.

mutalyzer/website/__init__.py

@@ -3,6 +3,7 @@ Mutalyzer website interface using the Flask framework.
 """
 
 
+import os
 import pkg_resources
 
 from flask import Flask
@@ -57,7 +58,8 @@ def create_app():
         'mutalyzer', 'website/templates/static')
 
     app = Flask('mutalyzer',
-                template_folder=template_folder, static_folder=static_folder)
+                template_folder=os.path.abspath(template_folder),
+                static_folder=os.path.abspath(static_folder))
 
     app.config.update(DEBUG=settings.DEBUG,
                       TESTING=settings.TESTING,