[Assignments] Increase 'Edit Assignment Dates' batch edit limit to 4 characters

[JSkelhon]

Problem statement:

In Assignments -> Edit Assignment Dates -> Batch Edit tool, the option to "shift dates" is limited to 3 characters. This means you can change due dates by up to 999 days, or just 2.7 years. We use 'parent' courses to simplify maintenance and copy these for each course run, but some are over 2.7 years old, so we have to apply the batch edit multiple times.

Proposed solution:

Changing the limit to 4 characters would give a limit of 9999 days, or 27.3 years - more than enough!

User role(s):

admin,instructor,ta