For compatibility in IE10/IE11 which don't otherwise "know" this element's role/don't expose it to AT

includes explicit `role="main"` for IE10/IE11 compatibility

For IE10 (and any older browsers) support , so at least the layout doesn't fall apart if author is using them.

* Split out/expand mention that base navs lack active styles
* Add accessibility notes for navigation bars vs dynamic tabbed interfaces

The link to package.json in the v4 docs was linking to package.json in the v3 source.  Fixed to point to the correct v4 location.  A change like this will need to be made for all branches on version 4 if you want the docs to be linked correctly (github may be smart enough to follow the link to the current branch if you are on github but it was wrong from the main site).

Should remove `data` not `class` on dispose

* Fix incorrect code indentation
* Remove unnecessary vendor prefix for `box-sizing` - all modern browsers now support this unprefixed
* Remove incorrect `<label>` and change static controls to readonly inputs
* Allow `<img>` elements without `src` to allow for `holder.js` images used in the docs, which lack `src` and use `data-src` instead