fix default content area height

As the window is maximized afterwards, using the window
height before to calculate the content area height leads
to incorrect results (same for window width). Use screen
width and height instead.

Also, use the content area height for the NavigationBox.
add more stuff on syntax
remove UTF-8 BOM
add missing XML declaration
more on syntax
delete empty part usage-cases
move UI related code in subdirectory
add new tmp directory and use it for temp files
small casing fix