Merge pull request #675 from houqp/master

Bug fix for screen rotate in crereader & fix from @kai777
add screen dpi property in koptcontext
update k2pdfopt to version 1.6.3
add libk2pdfopt as a prerequisite lib for kpdfview object
Merge pull request #676 from chrox/master

update k2pdfopt to version 1.6.3
Allow user to specify header font
1. Add Shift-H command to select page header font for crengine
2. Remove "(requires re-open)" from the Help of V command as it no
longer requires re-opening the file.
3. Replace the message "Redrawing" with "Formatting" as it describes
more accurately what is happening.
Merge pull request #677 from tigran123/creheadfont

Allow user to specify page header font for crengine
Modify those functions about the view_mode equal "page" when the kindle
in Horizontal screen state.
Merge pull request #692 from ZenRoi/master

Modify those functions about the view_mode equal "page" when the kindle in Horizontal screen state.