Add function call managment, also factorize code and remove old data formating functions

Created originally on Bitbucket by alorimier (Anael Lorimier)

Was already merged in Bitbucket before import, marked as merged by the import user

I added the managment of function call, using libreoffice links:

#!bash

py3o://function="myfct(py3o.myvar)"

This allow users to call any functions, as far as the function name is known by the server. We will certainly later add extension managment, so we can add/remove functions.

I also removed the old functionality of formating the value with a libroffice attribute.