Screen/SDL: remove Kobo support

The Kobo doesn't use SDL anymore.
Event/Console/Queue: check "running" inside the Wait() loop

Allows Quit() to be called from inside FileEventHandlers.
IO/Async/DiscardFileEventHandler: new helper class
Event/Console/Queue: use DiscardFileEventHandler

.. instead of deriving the EventQueue class from FileEventHandler.
OS/FileDescriptor: check __BIONIC__ instead of ANDROID
OS/FileDescriptor: add methods EventFD(), SignalFD()
Event/Console/Queue: handle SIGTERM and SIGINT
Event/Console/Queue: don't write to EventPipe if in UI thread
IO/Async/DiscardFileEventHandler: Fix compilation with gcc 4.6.2
Event/Notify: call ClearNotification() in the destructor

Reuse existing code.
NEWS: prepare for 6.6.4
Event/DelayedNotify: cancel the timer
Dialogs/FileManager: cancel the timer
Volkslogger IGC download. Increase timeout.

Increase the timeout to wait for the VL to calculate security for 5min to
10min.
See ticket #2910
Event/DelayedNotify: call ClearNotification() in the destructor

Reuse existing code.
Event/Notify: remove obsolete "friend" declaration
Event/Notify: disable destructor on Windows

The Window is destroyed automatically, and this will implicitly delete
all posted messages.
Event/Notify: disable Callback() on Windows

Unused.
Merge branch 'v6.6.x'
Event/GDI: make EventQueue a class

Prepare for migrating to TimerQueue.