Restructure pipelines and badges

- Seperate test pipeline into E2E, integration and unit test pipelines.
- Improve documenetation for pipelines (ci-cd.md).
- Introduce naming convention for worklow files and names.
- Center badges with multiple files on README file.

.github/workflows/tests.integration.yaml

@@ -0,0 +1,30 @@
+name: integration-tests
+
+on:
+  push:
+  pull_request:
+  schedule: # To get notified about problems from third party dependencies
+    - cron: '0 0 * * 0' # at 00:00 on every Sunday
+
+jobs:
+  run-tests:
+    strategy:
+      matrix:
+        os: [macos, ubuntu, windows]
+      fail-fast: false # So it still runs on other OSes if one of them fails
+    runs-on: ${{ matrix.os }}-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Setup node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 15.x
+      -
+        name: Install dependencies
+        run: npm ci
+      -
+        name: Run integration tests
+        run: npm run test:integration