Fix Dropbox updating to v1.6.15.

Quick update to prevent Dropbox upgrading to version 1.6.14.

Quick update to prevent Dropbox upgrading to version 1.6.13.
Additionally, the changelog was removed from the readme files and put in an own file called “changelog.txt” and a Dutch readme file was added (thanks to Sam Bouwer).

Just a quick update to fix the automatic update of Dropbox to version 1.6.11.

Changelog:
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1.5.1.0 (02.01.2013):
#Dropbox update prevention for 1.6.11
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