added /nbproject/

What does this MR do?

adding /nbproject/ to .gitignore regarding netbeans project folder (analog to .idea files for intellij)

How confident are you it won't break things if deployed?

Very

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))