added disable masks: supports business days and even/odd weeks; completed nl_NL translations

[bluppfisk]

nl_NL counts as nl_BE too btw

[bluppfisk]

I'm new to committing and this is my first JS project in a long while. I may be doing things wrong but that's mostly because all these new tools confuse me.

Still, added are a few functions to do the following:

1. completed the nl_NL translation (added labels)
2. set different weekday masks on odd or even weeks
   syntax:
   disable: [ { oddWeeks: [1,3,5], evenWeeks: [2,4,6] } ]
   in above example, the 1st, 3rd and 5th day will be disabled on odd weeks, while on even weeks the 2nd, 4th and 6th days will be disabled. It also takes your firstDay setting into account.
3. modified the { from - to } mask to take business days into account
   syntax:
   disable: [ { from: [2016,7,9], to: 3, toWorkingDays: true } ]
   in the above example, it will disable the next three business days after Saturday 9th and Sunday 10th July 2016. I.e. it will disable Monday 11, Tuesday 12 and Wednesday 13.

[bluppfisk]

Currently no experience with Grunt so I didn't update the minified versions of the JS.

[DanielRuf]

Please separate feature and i18n. And please rebase your master branch before creating the new branches from it.

[Pantaleaogc]

Hi.. How to disable specific days of each month, for the entire period, or the other way around, enable only specific days. In the specific case, I want only the 15th of each month to be chosen. Thanks for the feedback