(refactor) Purchase Order Registry refactoring functionality

[DedrickEnc]

The purchase order registry is reviewed and is in master branch, after trial here is points to address

1. Applying registry standard refactor: Invoice registry #1749

2. MODIFIER ETAT seems not useful and can not see how this can work with a purchase order of type PAYER LORS DE L'ACHAT and it is also easy to forget updating it!

These point can be discussed to have final point to address.

[jniles]

See as well #1746 which discusses point 1 in detail.

[DedrickEnc]

Can be closed, if there is a point not tackled, a separated issue can be created