Make counters definition less restrictive

In NCAPP-71, several restrictions exists:

• figure and table counters cannot be defined
• figures of type block and inline cannot share a counters

While those restrictions does not have to be enforced in XWiki rendering and with CSS based numbered content, this is not the case when pages containing figures with counters are exported, in particular to latex.
It might be possible to improve the latex generation to lift such constraints, while preserving other features like the possibility to have list of entities (e.g., list of figures, or list of tables)