#825 Improve dutch translation

[Rhythmdrill]

I found a spelling error in the dutch translation ('gebasseerde' should be 'gebaseerde').
I contacted the translator mentioned in the about dialog, He said I was right, but he didn't want to correct it himself. So, I checked out the sourcecode and corrected the file myself.
And while I was at it, I also completed most other missing translations.

[trialuser02]

Done. Thank you.
If you have interest to translate qmmp, you should use https://www.transifex.com/qmmp-development-team/