[IMP]Export Wizard: able to change sequence of fields in 'Fields to Export'

Hello,
I have improved code to able to change the sequence of fields from 'Fields to Export' column to move fields up and down.

More Details:
Task: https://www.odoo.com/web#id=6586&view_type=form&model=project.task&menu_id=3942&action=327
Pad:https://pad.odoo.com/p/r.FV11g0aCvb7u3XvR

Thanks,
rba-odoo
next time, don't forget to declare your variable with "var" (else you're creating a global!)
I'll fix it myself by merging