<th> alignment bug in IE

There's [a bug](http://haslayout.net/css/Non-Inherited-TH-Text-Align-Bug) in IE (including v11) that causes the `text-align` value on `<table>` to be ignored, resulting in the headers to appear centered:

![canon-th-ie-bug](https://cloud.githubusercontent.com/assets/979677/4378150/634347de-4355-11e4-9563-50a6f01a8e32.png)

(All other browsers show the `<th>` cells left-aligned)

A workaround is to set `text:align: inherit` on the `<th>` element. Searching the Canon code base, I didn't see any pattern for handling browser-specific quirks, so I dropped the workaround in-line with the rest of the `<th>` styling.