[3.0 release] Responsive off-canvas UI

HTML:
re-organized 'pages' to sections
removed class for fieldset
added mwspell.png in place of empty card holder

mycss.less:
re-organized styles wrt to the section they're in
removed class for fieldset, use selector

off canvas:
added offcanvas.js and offcanvas.css
section padding and positioning styles moved to offcanvas.css

 On branch gh-pages
 Changes to be committed:
	modified:   css/dev/mycss.less
	new file:   css/dev/offcanvas.less
	modified:   css/mycss.min.css
	new file:   css/offcanvas.min.css
	modified:   index.html
	modified:   index_dev.html
	modified:   js/dev/mwcardex.js
	new file:   js/dev/offcanvas.js
	modified:   js/mwcardex.min.js
	new file:   js/offcanvas.min.js
	modified:   mwcardex.appcache
	new file:   spells/mwspell.png