fix long floating content in pages

test plan (with draft state enabled):
 * create a wiki page with long floating content
   e.g. <div style="float:left">
 * add the page to a module
 * navigate to the page (through modules)
   - the progression Next/Previous buttons should not overlap
     the content of the page

fixes CNVS-12377

Change-Id: Id1ff73d61713aeac6c18733ae830d6ba3782d667
Reviewed-on: https://gerrit.instructure.com/34712
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>