Dutch translation fixes

[Remyoman]

Added AppCode related files to the gitignore file.
Fixed an issue in the Dutch translation that resulted in an underflow.

[1and2papa]

@Remyoman Thanks. I have manually merged the translations fix.

[Remyoman]

No problem, thank you for the fast handling.

One question: Why not add the appCode related gitignore lines?

[1and2papa]

@Remyoman I managed to put your PR in v3.1.0 update and not quite sure about what appCode actually is. I would be grateful if you could direct me more about it. Thanks.

[Remyoman]

Thank you for including the chanes in the latest release.

AppCode is an Xcode compatible environment which can be used to develop iOS apps. It makes use of the Xcode command line tools and tools that Xcode itself also uses. It can't replace Xcode, but it can take care of the coding aspect.

It is part of the Jetbrains IDE's which are all based on the same core which is open source if I recall correctly. You can find more information on their website. https://www.jetbrains.com/objc/

I will leave it at this before I go on a rant, I hope this satisfies your request.

[1and2papa]

@Remyoman thanks for your supplements, will merge it in next update. Thanks.