Feat 323 assignment bugs

[karimouf]

Overview

Three bug fixes around assignment revisions and assignment copying:

• The "max revisions" slider's unlimited sentinel collided with the newly-allowed "0 revisions" option
• The max-revisions error message exposed a confusing internal count
• Copying an assignment didn't record which assignment it was copied from

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Improvements

• Clarified the Maximum Revisions slider help text: N revisions means the original submission plus N resubmissions (e.g. 1 revision = 2 submissions total)
• Simplified the "maximum revisions reached" error message shown to users, dropping the internal (chainDepth/maxRevisions) count that could read as inconsistent with the revision terminology
• Assignment cards now show a "submissions left" badge and a due-date badge (moved into the card header, next to the upload button) instead of no indication at all
• Due-date badge turns orange within 24 hours of closing and red (with an "Overdue by ..." message) once the due date has passed, instead of always showing a plain, non-directional time difference
• "Submissions left" badge turns green once a user has 0 submissions remaining
• Users with the upload-for-others right see the due date for everyone but no longer see a personal "submissions left" count, since it isn't meaningful for them

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Bug fixes

• Fixed: the Maximum Revisions slider was fixed; the number described for each revision adding to your first submission we now can set the maximum revisions to zero, which means you only can upload one original submission
• Fixed: unlimited revisions is now set to -1 instead of a specific number
• Fixed: copying an assignment not recording its origin — parentAssignmentId is now set to the source assignment's ID when using "Copy Assignment", so copies stay traceable to their origin