Update and improve fe-ionic (master)

[cschweikert]

The following things in the current fe-ionic quickstarter have been updated, added or improved:

• ionic: 6.13.1 -> 6.19.0
• align code with fe-angular quickstarter including changes within fe-angular
• removal of certain workarounds needed by current version
• bring documentation up-to-speed

Fixes #780

Tasks:

• Updated documentation in docs/modules/... directory
• Ran tests in <quickstarter>/testdata directory

Please note

1. Ionic replaced TSLint with ESLint.
2. The unit testing capabilities are currently broken (see for exmple Quickstarter tests: Verifying Jenkins run attachments fails ods-core#1124 and Provisioning of projects doesn't setup Jenkins with Aqua credentials  ods-core#1125). I filled the gaps as good as I could with manual tests.
3. There will be a follow-up PR for the 4.x branch.