address XSS issues in KRecord swf files

refs CNVS-16682

test plan:

 - enter valid kaltura plugin settings
 - with "Use alternative flash recording widget" UNCHECKED
   - verify that media recording works properly
   - verify that steps listen in CNVS-16682 do not result in JS
     execution
 - with "Use alternative flash recording widget" CHECKED
   - verify that media recording works properly
   - verify that steps listed in CNVS-16682 do not result in JS
     execution

Change-Id: Ice6034da633de988eea3d58b9a13cab3ef288ae9
Reviewed-on: https://gerrit.instructure.com/45746
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Derek Hansen <dhansen@instructure.com>
Product-Review: Michael Ziwisky <mziwisky@instructure.com>
Reviewed-by: Michael Ziwisky <mziwisky@instructure.com>