cre: load document afer set font

Conflicts:
	cre.cpp
	crereader.lua
adapt ui to loadDocument before setFont
read header font from config
reset postInitCallback on ReaderUI:init
read LineSpace from config
save header_font_face
save and restore gamma_index for crengine
pass filename properly for zipped fb2 in CreDocument:init()
Merge pull request #709 from houqp/new_ui_houqp

couple of enhancements to crengine