Order groups

issue: http://issues.qcadoo.org/browse/QCADOOMES-121

Brief

A simple module that allows us to group production orders:

• number and name are mandatory, the rest is optional
• every order inside a group must have it's start/end dates between the groups start/end dates
• the end and start date of an group may not be set
• the table should have and option Show orders that moves us to the Orders table filtered to the orders to the group

This module should also modify the behavior of the orders module:

• add the ability to select a group when adding an order
• add the column Group name in the Orders table
• add the option Group to the Orders table that groups the selected orders

Mockup