Remove trailing whitespace characters and add .editorconfig

Hello!

I noticed some source files contain trailing whitespace characters... Which can make navigation a bit annoying :)

This removes them, and additionally adds an .editorconfig file to aid in enforcing some basic styling rules across different IDEs and text editors. I based the .editorconfig styling rules on what the project appears to be using already: 4 space indentation, lines terminated by line-feeds and utf-8 encoding.

Most files also did not insert a final newline, which can pollute diffs, and cause some other issues.

EditorConfig is a file format that is supported by the vast majority of modern text editors and IDEs. More information can be found here: https://editorconfig.org/