Create a test to make sure ajax forms can be submitted with custom date order

Created new FunctionalJavascript test for testing widgets and ajax, added test case for date part order. Made sure that test fails without #2973037 changes. To implement test I also added datetime_extras_test module which installs CT with datetime field which I use for test.
Also in the module I'm adding Ajax rebuild button which simply rebuilds whole node add form for this test CT.
In test case I check order with :nth-child and make sure it stays the same after rebuilding form with ajax.

Automatically closed - issue fixed for 2 weeks with no activity.