[Proposal] Adding editorconfig

[JaeHyeon]

Editorconfig(https://editorconfig.org/) is a config file that contains file
format defining coding style, such as `trim_trailing_whitespace` option to
remove trailing whitespace of the code, which is redundant.
Also, options can be applied seperately between different file formats. For
example, we can define different coding style between Java and Scala.
How about using editorconfig in Nemo repository?