Fix visual bug with large file error msg in cms.

[ataki]

This hotfix patches the functionality of the GridFS PR described by @sarina here: https://github.com/edx/edx-platform/pull/5731 by dismissing the error msg when the user uploads a large file and fails, then uploads a regular file. This includes a Jasmine test to cover this case.

[openedx-webhooks]

Thanks for the pull request, @ataki! I've created OSPR-324 to keep track of it in JIRA. JIRA is a place for product owners to prioritize feature reviews by the engineering development teams.

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[singingwolfboy]

Hey @ataki, we had an issue on the master branch recently, which seems to have caused some problems with the commits on this pull request. Can you rebase your pull request so that the extra commits no longer show up?

[ataki]

sure, just rebased on top of master as of 12/29

[singingwolfboy]

Hey, sorry for the delay on this. I just manually tested your pull request, and it works great! Thanks!