Modified Footer Display Option; Added hover style to links

The option to not show the footer now makes the theme link appear at the bottom of the sidebar.
The theme link, in both the footer and the sidebar, now opens in a new window or tab.
A new "centered" class was created to center links if desired.  This is used on the theme link in
the sidebar.  Links now italicize when hovered over.
Fixed sticky footer bug.

Poststream now right-aligns via a fixed margin rather than a right float.  Also added some
window-size dependent changes to footer to make it more readable in small window mode.
Added dropshadows to posts, sidebar and header.
Header does not italicize when hovered.