Lilypad: Better focus/capture/uncapture handling.

1. After ALT-Tab to another window and back, now it accepts PCSX2
shortcuts properly (e.g. Esc or F6 etc) - focus changes were not
always recognized before.

2. If Lilypad is set to capture mouse, now it releases it on Escape. This
part is a small hack because the code looks as if it should handle it,
but in practice doesn't. This adds explicit uncapture on Escape.