Add SAST security checks with SECURITY.md #178

This commit incorporates Static Analysis Security Testing (SAST) using
CodeQL. This integration will enforce consistent security assessments
with every change and on a predetermined schedule.

This commit also involves a restructure of security checks. The existing
security-checks workflow is renamed to better reflect its functionality
related to dependency audits.

These changes will enhance the project's resilience against potential
vulnerabilities in both the codebase and third-party dependencies.

Changes include:

- Remove older LGTM badge that's replaced by SAST checks.
- Rename `checks.security.yaml` to `checks.security.dependencies.yaml`,
  reinforcing the focus on dependency audits.
- Update `README.md`, ensuring the clear representation of security
  check statuses, including new SAST integration.
- Add new `SECURITY.md`, establishing the protocol for reporting
  vulnerabilities and outlining the project's commitment to robust
  security testing.
- Enhance `docs/tests.md` with detailed information on the newly
  integrated security checks.
- Add reference to SECURITY.md in README.md.

.github/workflows/checks.security.dependencies.yaml

@@ -0,0 +1,22 @@
+name: checks.security.dependencies
+
+on:
+  push:
+  pull_request:
+    paths: [ '/package.json', '/package-lock.json' ] # Allow PRs to be green if they do not introduce dependency change
+  schedule:
+    - cron: '0 0 * * 0' # at 00:00 on every Sunday
+
+jobs:
+  npm-audit:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Setup node
+        uses: ./.github/actions/setup-node
+      -
+        name: NPM audit
+        run:  npm audit --omit=dev