KCanvas and IValueProvider should provide time bounds to downstream

[michael-burk]

Clips should ba able to inherit their length from children: So if I create a clip (Foo) in a compositor (A) and connect another compositor (B) to it, the clip length of "Foo" is defined by the time between the start of the first and the last clip in compositor (B).

Clips should have the abillity to be be linked, so that their start and endposition changes dynamically, if one of them is shrinked or expanded. So if one clip down in a nested timeline/compositor is changed, you don't have to manually change every single clip in the tree.

[natan-sinigaglia]

there would be an option in the Ctrl clip of timeline/compositor to inherit bounds from source