Let imgcache.js work with encoded URI's 

I'm using imgcache.js in a Cordova application. The URI's of the images are retrieved from a JSON datasource, which provides encoded URI's. However, the Helpers.sanitizeURI always re-encodes the URI, which leads to double encoding. For example, this URI:
http://10.2.1.37:3000/api/avatars/137/The%20Dude_avatar.png

is encoded into:
http://10.2.1.37:3000/api/avatars/137/The%2520Dude_avatar.png

which is the incorrect URI for that image. 
I've solved it by adding an option to skip URI encoding, which is disabled by default.