Update and improve the Dutch translation

[SKBotNL]

Update and improve the Dutch translation.
I've tried my best to add missing translations, fix spelling and grammar, and make everything more consistent overall.

[AlexanderVanhee]

Please try to follow the capitalization method of the original.

See this HIG guideline for more info:
https://developer.gnome.org/hig/guidelines/writing-style.html#capitalization

[SKBotNL]

Please try to follow the capitalization method of the original.

See this HIG guideline for more info:
https://developer.gnome.org/hig/guidelines/writing-style.html#capitalization

Title case is I believe an English-exclusive concept, it makes no sense to use it in localisations.

[SKBotNL]

I also want to add that that rule does not seem to be followed in (all) other translations either. I've specifically removed title case from this translation because it does not make sense to apply a rule for English to Dutch, or any other language for that matter.

[SKBotNL]

I've made one minor change to consistently use ’ instead of ' in all the Dutch translations.

[kolunmi]

everything ready here?

[SKBotNL]

Yes

[kolunmi]

Thanks!