NLA transition interpolation profile

There should be an option in the auto transition in NLA to choose a profile curve instead of being stuck with the linear transition, or having to animate it manually. The same should be the case for the "transition" strip.

There is no need for transition frame start and end option because its a transition between two action strips, so it has an already defined start (the end of the previous strip) and end (the beginning of the next one). having a profile for transition would be waayy more useful.