Fix linking

[K-Meech]

For #1116

This PR:

• Fixes linking images within the project creator (uses absolutePath if the image is outside the project directory)
• Fixes remote metadata creation
• Fixes failing project creator tests + adds more for linking / remote metadata
• Updates the javadoc

Note: I've currently commented out the line in ImagesCreatorTest that validates the dataset json against the schema. This is due to the missing absolutePath. It can be un-commented once this is added.

Also, this doesn't currently support directly giving an s3address to the project creator (for files that are already stored remotely). This is probably best added later, as it's a new feature that wasn't in the original project creator.

[K-Meech]

Here's a link to the PR to add absolutePath into the schema: mobie/mobie.github.io#110

[tischi]

Thanks a lot @K-Meech ❤️ !

I created an issue for the S3 linking: #1130