themes lib MDL-24895 Multiple fixes to better handle overflow.

Major tasks undertaken in this patch:
* New format_text argument, overflowdiv.
* New page layout Report.
* Review of all format_text calls.
* Added support for the report layout to all themes.
* Changed forum post display from tables to divs.

blocks/html/styles.css

@@ -0,0 +1,2 @@
+.block.block_html .content {padding:0;}
+.block.block_html .content .no-overflow {padding:4px;}