fix broken URLs and automate broken URL checks #70

This commit:
- Fixes broken URLs using archive.org or other references.
- Replaces tenforums.com URLs with better documentation as they tend to return HTTP status code 403 to tests and also are low quality source.
- Changes all insecure http sources to https alternatives
- Adds integration tests to check for broken URLs
  - There's logic implemented for having a delay inbetween when sending requests to same domains, however it's not used as the sources can respond to totally parallelized requests.
- Run test pipeline weekly to get notified about broken URls without commits

package.json

@@ -30,6 +30,7 @@
     "@juggle/resize-observer": "^3.3.0",
     "ace-builds": "^1.4.12",
     "core-js": "^3.9.1",
+    "cross-fetch": "^3.1.4",
     "file-saver": "^2.0.5",
     "inversify": "^5.0.5",
     "liquor-tree": "^0.2.70",