Updates to getPrice to either include or exclude tax

Also redirect to a route rather than the URL (I've wanted to change the URL that the route points at and redirecting to a URL breaks this).
It's done like this to be consistent with getExtPrice function which has the parameters in the same order as I've set these as. I thought consistency was more important at this stage than BC. It is a minor break of BC however but considering no one is using this module except for me/us I can see no issue with it. I've also checked everything else internally that uses this functionality and it causes no breaks against the existing tests and functionality. These parameters are "modifiers" to the default functionality and have not been used anywhere in speck.