Fix/layoutcheck distance image writing

[martingrossmann]

Description

Executing a test with gradle -p <subproject-dir> test causes a mismatch of the working directory. It is still the project root dir but the subdirectory is needed.
org.apache.commons.io.FileUtil.FileUtils can handle this, but not ImageIO. This was the only place in the code where images were not stored in a temporary directory.

I also fixed the check of image dimensions which causes multiple optional assertions in the report.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules