Implementation of the timeline

[JeremyMeissner]

The user must be able to navigate in a timeline and add keyframes. He must also have easy access to the different keyframes.

• Creation of a panel to manage keyframes
• The addition of a keyframe saves the state of the modified elements (addition of a symbol at the level of the parameters to know which elements/parameters are in a keyframe)
• An interpolation is created for elements that have modified states in at least one keyframe