ENH: begin reworking doxygen to use xhtml/css and new OpenCFD look

- drop old table-based formatting in favour of div.
- use single css with @import to minimize the impact of style changes
  on the html documents themselves.
- separate css/ directory
- locate css graphic elements inside the css/ directory for easier
  relative addressing.

doc/doxygen/_Footer

@@ -0,0 +1,9 @@
+  <!-- end of doxygen-generated content -->
+  </div> <!-- main -->
+  <div class="footer">
+    Copyright&nbsp;&copy;&nbsp;2000-2010&nbsp;
+    <a href="http://www.openfoam.com/about">OpenCFD Ltd.</a>
+  </div>  <!-- footer -->
+</div>  <!-- page-container -->
+</body>
+</html>