Adds urlencode filter to CreativeConfiguration

This filter will perfom an urlencode over UTF8
and non UTF8 strings. Ie :

%{bidrequest.device.carrier#urlencode}
Merge pull request #160 from Motrixi/utf8urlencode-filter

Adds urlencode filter to CreativeConfiguration
Merge pull request #9 from rtbkit/master

Downstreaming urlencode filter changes