Normalize whitespace in source files

Ensure that no source files have trailing whitespace at end of lines and ensure that all files end with a single trailing newline.

This also adds Github Actions to enforce whitespace conventions.

.github/workflows/ci.yml

@@ -81,6 +81,17 @@ jobs:
         run: |
           cd src/
           pycodestyle
+  whitespace:
+    runs-on: ubuntu-20.04
+    steps:
+      -
+        name: Ensure there are no trailing spaces
+        run: |
+          .github/workflow-scripts/check-trailing-whitespace
+      -
+        name: Ensure all text files end with a trailing newline
+        run: |
+          .github/workflow-scripts/check-trailing-whitespace
 
   tests:
     runs-on: ubuntu-20.04
@@ -158,7 +169,7 @@ jobs:
         path: src/documents/static/frontend/
 
   build-release:
-    needs: [frontend, documentation, tests, codestyle]
+    needs: [frontend, documentation, tests, whitespace, codestyle]
     runs-on: ubuntu-20.04
     steps:
       -
@@ -268,7 +279,7 @@ jobs:
   build-docker-image:
     if: github.event_name == 'push' && (startsWith(github.ref, 'refs/heads/feature-') || github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/ng-'))
     runs-on: ubuntu-latest
-    needs: [frontend, tests, codestyle]
+    needs: [frontend, tests, whitespace, codestyle]
     steps:
       -
         name: Prepare