Improve end-to-end testing

[otacke]

• Add test content parameters as assets and dynamically build content instead of requiring prebuilt H5P content files
• Add github workflow
• Find a good way to switch between local testing in an H5P CLI tool context and remote testing in a github workflow (and local testing outside of an H5P CLI tool context?)
• Improve code im general
• Add a server start and a server stop command to the H5P CLI tool to allow it running in detached mode.