Ensure consistent formatting of code and xml

[dr0i]

There is no consistent formatting of code (and xml? etc.).

• [ ] agree and document on how to format code
• [ ] at best find a solution to ensure all the different IDEs use this code formatting
• [ ] at least ship a template for eclipse users to use these formattings

[dr0i]

There is a .editorconfig since 9988ed377627aef60495a9ca9a2d4d26b5f78fbb. Look how to reuse this e.g. in eclipse.

[dr0i]

This is handled by https://github.com/metafacture/metafacture-core/pull/388. .editorconfig is supported widely, e.g. for codium. Closing.

[blackwinter]

Thanks! Didn't know - and, admittedly, didn't check - there already was an issue for this.

[dr0i]

This came up again at https://github.com/metafacture/metafacture-core/pull/413#issuecomment-964011789 ff.

We'd have to look into code formatters, I suppose. (Spotless may be an option.)