Motivation

1. It is not very obvious to the users why this frame is needed
2. It is very inobvious for the user when you delete this frame explicitly, but it creates back
3. Moving the first frame with D&D can make you brain overheat, when trying to understand what happens there.

Implementation Requirements

1. Keyframe channel should be available in the paint layer (and paint device), if and only if there is at least one frame available in the paint device. When the last frame is deleted, the paint device (and the layer) should become non-animated. And therefore the onion-skins option should disappear for this layer
2. In KisPaintDevice there should always be an empty m_data, which is returned for the frames that are not present in the list (before the first frame).
3. When the user starts painting on an no-frame area (that is handled by m_data) a new frame should be created automatically, even when auto-frame feature is turned off.
4. To achive some kind of thread safety, m_data must not change its pointer value throughout the entire life of the paint device. It must always be valid.
5. When the number of frames is non-zero, m_data should represent an empty paint device. When no frames are available, m_data should contain real user data.