Fix Contributor Upload/Reupload Redirect

[yizou275]

The current contributor upload/reupload page backend is implemented in PR #780. However, the behavior of the page after the form is submitted needs further refinement. The current code plans to redirect to the knowledge base landing page, but sometimes fail to work (the page remains the same when the form is successfully uploaded and backend correctly updated).
Need to decide between: (1) show a "Successful Submission" page; (2) redirect to some other existing page.
If choosing (1), need to design and implement this page; if choosing (2), fix the current redirecting bug and link it to the page.

[mrollinswaterman]

Added code to views.py to redirect the user back to their contributor dashboard upon form submission. I used Django's built-in redirect function to point the user back to the correct page.

[mrollinswaterman]

Closed by PR #954 .