bug fix: read css file name instread of content in cre:setStyleSheet
API changes in cre.cpp

* now css argument is removed from newDocView call.
* when setStyleSheet method cannot read given css file, it
  clears all the applied style.
* add setEmbeddedStyleSheet method.
add css menu and save/restore css settings
add embedded css toggle and some other fixes
redraw current page when exit from css menu
Merge pull request #727 from houqp/master

add css menu and embedded css toggle