[FIX] l10n_be: Fix BS and P&L

Multiple fixes in Belgian BS and P&L:
* Forgotten accounts
* Missing or empty sections
* Missing or wrong signs

Additionally, changes to the CoA in order to properly feed the BS and the P&L
so, here i've a problem.... Because as a developper i found more "true", to show the balance of the accounts like the debit - the credit. No trick, a simple sum. But i assumed that was only because i was reasonning like a developper, so i asked Christine, and she said "i prefer to see negative amounts because it comes after the assets and i want to see the difference between!" (end of citation).

So i'd reject those changes too, even if i agree that for other people it might seem a mistake...