Add support for editing URIs

Send two URIs for each tracked item UI to the client, and allow
updating of two URIs in the PATCH request.  Why two?  Meh.  Seemed like
two would be enough.
Add google play store support for price

Add an expression which should work for the google play store to find
the price.  Don't worry about finding the category or name of the item,
since we can use amazon for that (or just manually enter it).