Add m_lastLockFrameCount and m_lockPaintFrameCount, compute frames
painted while the screen was locked and log the values. Show frame
counts in the lock info overlay, record frame count at lock, and reduce
the lock info font size for better layout.
Record lock time, duration and count in CustomWidget and show a
lock-info overlay. setPaintingEnabled now logs lock/unlock times and
increments lock count. Emit screenLocked/screenUnlocked signals in
ScreenLockDetector. Minor UI and whitespace cleanup.
ubuntu1804