Timeline: Esc key deselect the selected range of frames/layers
Add ability to change the properties of several frames (a range of frames) at once
Fix some compilations problems in MinGW

Anyway without DirectX header files (ddraw.h specifically) we cannot
compile Allegro source code with MinGW.
StandbyState::onUpdateStatusBar(): show frame duration
Timeline: add status bar text when we hover different elements