This will help drawing the high contrast mode and makes the plus more
visible even given the background color.

Signed-off-by: Tomas Chvatal <tchvatal@suse.cz>

Thanks cppchecker for  detecting this

When in a header and hitting Ctrl+PgDown, go to the end of the page if
there is no footer in it instead of staying in the header. The same case
for footers has been fixed too.

Removed the cursor positioning hackery in ToggleHeaderFooterEdit(): this
is now handled by the caller.

Show the Header/Footer edition when hitting Ctrl+PgUp and Ctrl+PgDown
and actually landing into a header or footer.

Moved the ChangedHeaderOrFooter method from SwTextShell to SwWrtShell
for it to be accessible from the SwHeaderFooterWin objects... and that
method didn't really need to be in the root shell.

That fixed a few quirks from the copied code in SwHeaderFooterWin.

Changed the following:
 + Draw a gradient in the separator tabs background
 + Draw a solid line under the dotted one to have a contrast for some page
   background colors.