Samigo > format dates consistently in submission notification email

The current email notification sent out when a user submits a quiz has some inconsistently formatted dates:

The following assessment submission was recorded by Sakai:

Site Title : Discussion 3 SMPL101
Assessment : due date

Student : 0061 Student (student0061)
Submission ID : 8
Submitted on : 2018-Dec-15 12:23 PM
Confirmation Number : 8-17-98871f2b-bbb3-4c6e-b047-446c163792fa-Sat Dec 15 12:23:23 EST 2018

Assessment Due Date : 21-Dec-2018
Site ID : 636d17b2-3980-4230-b560-c85e1fcece23

—
This automatic notification message was sent by Sakai (http://localhost:8080/portal)
Control what email notifications you receive at Home -> Preferences -> Notifications

The "Submitted on" and "Assessment Due Date" fields use two different date formats. Let's be consistent here. After this PR, the dates in the email should be consistent:

The following assessment submission was recorded by Sakai:

Site Title : Discussion 3 SMPL101
Assessment : due date

Student : 0062 Student (student0062)
Submission ID : 9
Submitted on : 2018-Dec-15 12:43 PM
Confirmation Number : 9-17-a2e80501-2186-4a44-8821-1906df8cdb12-Sat Dec 15 12:43:16 EST 2018

Assessment Due Date : 2018-Dec-21 07:00 PM
Site ID : 636d17b2-3980-4230-b560-c85e1fcece23

—
This automatic notification message was sent by Sakai (http://localhost:8080/portal)
Control what email notifications you receive at Home -> Preferences -> Notifications

This issue was originally fixed in via cc2143b, but then regressed in as well, via 1f47624.