Add full view

Added the option to toggle full view, from markup view to preview.
It supports multiple files each with it's own view.
Here are a few screenshots:
http://screencloud.net/v/DZao
http://screencloud.net/v/fnp9
http://screencloud.net/v/h0YJ
Signed-off-by: Marco Rivadeneyra <rockiano@gmail.com>