Effects are now handled by an EffectUser class. This class handle
loading, saving, adding, initializing and applicating of any effect that
will be added to a class that inherits EffectUser.

This will avoid too many copies when dealing with GUI.

It shows the loaded effects list, and allow the parameters to be edited.

This disable global effects addition.

When a trackId is stored, we should use a signed type, as it can be
initialized in some error cases. My apologies to etix :)

Improving move detection, so that a clip that's moved to its old
position won't trigger a new (useless) action.

Signed-off-by: Ludovic Fauvet <etix@l0cal.com>

Fixes split undo/redo

This can't be the right way.