Add apache URL encoder

See #504 .

* update guava to have access to UrlEscapers
* add function in morph to encode item
* add morph function description
* add schemata used to include morph function
* update test file
Why is it called `apache-urlencode`? It doesn't use the Apache library. Even if it did, I think including the library name is not so nice. How about `urlescape`? And in general: are all these new files (properties, xsds) needed because this is our first custom morph function?