Switch libdazeus to a new JSON library called "jansson", maintained by Petri Lehtinen.

* UTF8 handling is a bit different now: the library will never send \uXXXX codes, but will immediately send UTF-8 as is (so "ƒøø", for example, instead of "\u0192\u00f8\u00f8").
* The workaround for broken libjson code has been removed!