Improvements for sim-a11y-view.html template

[samreid]

I noticed a few issues in the sim-a11y-view.html template. I'll mark them here as checkboxes, then assign to @jessegreenberg for work. After the work is complete, the actual sim a11y HTMLs should be regenerated and committed. This was discovered during phetsims/friction#64

• Typo in ineficient
• intervalId is never assigned to a var, and hence is getting assigned to window as a global.
• typo in the last word in this phrase: // set focus to the loaded ifram
• variable is never used: var politeElementContainer = document.getElementById( 'polite-element-container' );

[jessegreenberg]

Thanks @samreid, fixes made in the above commits. I regenerated a11y views with
perennial/bin/for-each.sh accessibility grunt generate-a11y-view-html and pushed. Closing this issue.