Provide a .editorconfig file

[hendrikebbers]

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👾 Description of the issue
We should add a .editorconfig file to IcedTea-Web (ITW) . See https://editorconfig.org/ for he definition of such file. This is based on a discussion in #679 and the PR contains the info how such file can be created in IntelliJ. For now we use the default formatting of IntelliJ. This should not change in future but should be backed by such .editorconfig for other editors and developers that have changed the default format in the IDEA.

📋 Step by Step
To solve this issue and contribute a fix to IcedTea-Web you should check the following step-by-step list:

🙋 Claim this issue: Comment below.
🍴 fork the repository in github by simply clicking the 'fork' button.
⤵️ check out the forked repository
🔀 create a feature branch for the issue. We do not have any naming definition for branches.
💾 Commit your changes.
🔀 Start a Pull Request.
🏁 Done 👍 Ask in comments for a review :)
🔬 If the reviewer find some missing peaces or a problem he will start a discussion with you and describe the next steps how the problem can be solved.
💥 you did it! We will merge the fix in the master of the IcedTeaWeb project.
💐 Thanks, thanks, thanks for being part as an open source contributor for IcedTeaWeb

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[stonefix]

Hi! Please, assign to me)

[hendrikebbers]

Done. If you need any help just ask here in the issue or at our slack channel.

[stonefix]

Ok, i tried it in PR #684