Added option to clean the URL.

Option is on by default.
More coherent naming of used variables
Collapsed a text box.
Added very basic affiliate tagging

If this turns out to be more hassle than what it's worth, I'll remove this later.

There's also a new setting that turns this feature on, or off. It off by default.
New setting in helper that allows to turn on adding of affiliate tags to Amazon and iTunes links.
Merge branch 'new-link-improvements'