Megamenus and adding masonry.

Ben, the Megamenu CSS has been simplified but I haven't translated into SCSS, would be good if you can do that. Other than that, the bare bones are in there and working.

Also, replacing isotope with masonry because full isotope functionality (which includes masonry) is not required - only the layout engine - so it's smaller.

Brought it all together into a main.js script which includes an ATSE namespace, not sure how you were thinking of going about that but that's what I've done :).
Making references relative (not absolute at root)
Implement mega menu

Megamenu disappears on hover

Signed-off-by: Ben Bailey <ben@happycontent.com.au>