VE-164: control large tables with overflow instead of popups.

https://wikia-inc.atlassian.net/browse/VE-164

This changeset introduces a new method of handling large tables. Instead of using the "jagged edge with popup" technique that we have now, it will use `overflow: auto` to control excess content which can be easily scrolled cross-browser using arrow keys when the scrollable content is selected, or using the shift key + scroll wheel to scroll horizontally (except in IE where it navigates forwards/backwards through history instead). If a table is wider than the article space it occupies, an additional class will be assigned via JavaScript that will provide a gradient on the right side of the scrollable area to denote that there is more information off screen that can be scrolled to.

The benefits of this functionality are that tables that are wider than the article content space are automatically handled when the page is rendered so there is no jumpiness (as opposed to being controlled strictly by JavaScript, which is the case now). This will also work nicely with the new fluid content area.