increase qunit coverage of mediawiki.html and mediawiki.util

increase qunit coverage of mediawiki.html and mediawiki.util

- mw.html
 * Adding test for mw.html.Raw
 * Adding more tests for mw.html.element

- mw.util
 * Minor coding style update (local variables)
 * Updating mw.util.addPortletLink to not create its own "#mw-panel",
 this was previously done for ./qunit/index.html (which has been
 removed) but when ran on [[Special:JavaScriptTest/qunit]] it collides
 with the existing "#mw-panel", so far didn't break anything but that
 was purely lucky. This element is redundant so taking it out of the
 html sample
 * Removing redundant clean up, #qunit-fixture is automatically cleaned
 after each test

Change-Id: Iaf9791ca3cdcac1b732c851cdecc8fcd9f96fdd8