Style cleanup.
app_server: Added NormalMouse() and ClickToFocusMouse() methods.

* Made FocusFollowsMouse() inline.
* For convenience only.
app_server: reworked SetFocusWindow() logic a bit.

* The normal mouse mode now only uses the window that had focus last if that
  window is one that does not support to be the front window (such as the
  desktop).
* This should keep the logic of r41264 without the drawbacks (see #7280 for
  more information).
* Added _WindowCanHaveFocus() method.
* This should fix #7630.
HttpHeaders: header field names are case insensitive.

Whitespace before and after tokens should be ignored.