Theme editor font sizing and layout errors

[ionfish]

This patch makes the theme editor present its fonts in a more Safari-friendly way (currently the code in the textarea is very small); I've followed the convention elsewhere to set the fonts in pixels, but I can attach an additional patch to allow resizing in IE6 if required.

Additionally, when the list of files is longer than the textarea, the "You need to make this file writable" text overflows the left column into the list of files. The attached patch restricts the text to the left column.

(In [6890]) Theme editor font sizing and layout fixes from ionfish. see #5890

Also, after doing "Update File" the confirmation message at the top messes up layout.

Needs testing in Internet Explorer; works ok on Saf3/Mac and FF2/Mac.

(In [6908]) Theme editor layout fixes from ionfish. see #5890

I don't have IE, but committed to make it easier for those that do to test.

From the tester's list:

On the "Theme Files" list, an unneeded </small> tag is included after
the "nonessential" span.

<li><a href="theme-editor.php?file=...">404 Template <span class='nonessential'>(404.php)</span>/*</small>*/</a></li>

(In [6960]) Remove extraneous tag. Props ionfish. fixes #5890