replace json-glib with jansson

[paolostivanin]

jansson supports custom memory allocation, meaning that gcry_calloc could be used to allocate secure memory. Right now, the data parsed by json-glib is not stored in a secure memory location.

http:https://jansson.readthedocs.io/en/latest/apiref.html#custom-memory-allocation

[paolostivanin]

This is now high prio, moving to 1.1.0. The export feature has been postponed.
The porting will require some time because it's a big refactoring that has to be backward compatible with the current implementation.

[paolostivanin]

An alternative would be to store the secret encrypted and then it will be decrypted only when needed. This, of course, will add an overhead, especially if a lot of tokens have to be updated every 30s...

[paolostivanin]

I'm currently rewriting the code to use jansson. Using this library instead of json-glib gives also more flexibility and helps to reduce the amount of code :)

I will also take this opportunity to carefully review all the memory usage and allocation 👍

[paolostivanin]

porting done, testing it right now