Make autoMerge way more readable

[Langomatisch]

Overview

I find it difficult to work with PlotModificationManager#autoMerge because the code is full of code-duplications.

This way its more readable and needs to be less maintained.

Description

I removed all code-duplications out of that method.

Submitter Checklist

• Make sure you are opening from a topic branch (/feature/fix/docs/ branch (right side)) and not your main branch.
• Ensure that the pull request title represents the desired changelog entry.
• New public fields and methods are annotated with @since TODO.
• I read and followed the contribution guidelines.

[TheMeinerLP]

Have you tested it ?

[Langomatisch]

Have you tested it ?

Yes i have tested it on a local server

[TheMeinerLP]

If you have some time over and be cool when you can add it for this an unit test 👍🏻

[Langomatisch]

Sure thing! I will do that in the evening :)