DDCUtil: Add support for multiple devices

Changes:

• new displayIds() returns supported display IDs
• detect() now returns suported display IDs for convenient
• brightness(), brightnessMax(), setBrightness() now accept an display id
• Remove animation handling since we already do that in PowerDevilUPowerBackend Replace event filter with a read/write lock
• Update PowerDevilUPowerBackend to use new DDCUtil interface

Tasks:

• What to use as display identifier