adds Dutch language

[gerbenjacobs]

Adds informal Dutch translations.

• Informal in the sense of "je" instead of "u" and still playful messages
• Discussions are translated as "discussie" as opposed to "topic"
• Responses are translated as "reacties" as opposed to "post"
• All capitalization mid sentences has been removed, this is not common in Dutch (i.e. "View The Discussion" becomes "Bekijk de discussie")
• I removed the 'blamey' part in the tampering alerts and just replaced with the technical "You can not edit|delete this post" (I looked at the code and it only happens when the user IDs don't match)

Also fixed a typo in the English email translation file.

Change-Id: If998471e04a59dc901fea4d7f98df235bfa721e3