It is of very limited practical utility currently, and will soon be
impossible to support due to more accurate memory map emulation.

Logging: check for filter before sending to the queue, to skip all heavy formatting on the other thread.

In various menu options letter cases were not consistent. This was also
the case within various debugging widgets. This attempts to make letter
cases consistent, but it is of course a matter of opinion which way is the
correct one.

Only allow manually setting focus to the rendering widget when in Single Window mode. Apply this behavior to when changing the mode while an app is running.

By default widgets are set to the focus policy Qt::NoFocus which disallows manually focusing it. Changing the policy to allow clicking the widget to set focus to it allows for keyboard input when not rendering to a popout window. This commit also sets focus to the widget when showing it.

Fixes issue #158.

The window title is none of the emulation core's business. The GUI code is free to put whatever it wants there.
Providing properly thread-safe window title getters and setters is a mess anyway.

Also moves system initialization to when the game is booted.