Update propal.class.php

it's this->lines who used on create propal function not this->products
add filter to effectif select
Qual: Removed useless method

The method is already in the DoliDB base class
Qual: Moved duplicate methods to base method
Fix undeclared variable
Qual: Moved duplicate method to base method
Hide a column that is always 0.
Qual: Prevent potential JS injection
Fix : proposal validation was converting third as customer
Merge branch 'develop' of github.com:Dolibarr/dolibarr into develop
Qual: Better type check
Qual: Removed useless assignment from void method
Qual: Undeclared variable replacement
Qual: Wrong variable name
Qual: Wrong type in method documentation
Qual: Missing variable declaration
Qual: Mistyped class property
Qual: Wrong type in method documentation
Qual: Wrong type in method documentation
Qual: Missing global declaration