[15.0][IMP] mrp_project_analytic_purchase: change function due to improved mrp_project_analytic

[ChristianSantamaria]

Change function due to improved mrp_project_analytic

[dalonsod]

@ChristianSantamaria rebase made due to #117 and #118

[dalonsod]

I see this:

• _get_from_child_acount_move_lines() is called from mark_analytic_mrp_from_child() for a certain productiom.
• So the code that obtain a new set of journal items and set for them the new check analytic_mrp_from_purchase could be simply moved from _get_from_child_acount_move_lines() to mark_analytic_mrp_from_child().
• With this refactoring, _get_from_child_acount_move_lines() will still represent a getter method, and not a getter & updater method.

What do you think @ChristianSantamaria ?