Handle URL parameter parsing at /parameters

All [these](https://github.com/bspatafora/java_server/blob/master/test/com/bspatafora/core/helpers/URLTestParameterized.java) were the result of RGR. I was building them up incrementally, and at a certain point figured switching to something like this would make it a whole lot easier to read.

This test was the evolution of a separate kind of test (maybe the 3rd or 4th when I was TDDing this method) that made sure the method could decode a string containing a variety of different percent codes, rather than just each one individually.