Provide .editorconfig in project to ensure consistent formatting

[Oliver-Loeffler]

Scene Builder code follows a certain formatting style. E.g. spaces are preferred over tabs. Add a notice either to README.md or to CONTRIBUTING.md, that Netbeans, Eclipse and VSCode require a plugin and IntelliJ does not. Add a link to https://editorconfig.org/.

Expected Behavior

When Scene Builder project is opened in IDE, code formatting rules and styles are imported from .editorconfig. Let Maven run the required checks (additionally to check style) editorconfig-maven-plugin.

Setup t o start with setup:

• no tabs, just spaces, 4 spaces indent, default line break to \n for *.java, *.css and *.properties
• add or complement README.md or CONTRIBUTING.md with a section on how to properly setup development environment

Current Behavior

When Scene Builder project is opened in IDE, existing formatting conventions in IDE may break existing format in files.

Context

Code formatting and use of spaces/tabs is a recurring issue in PRs and is time consuming and annoying for contributors and reviewers.