Tween looping and import fixes

Fix importing clips (vs groups) from the Editor. 

In the Editor, there are two ways of applying end-action for a collection of layers:

- If this collection is just a _folder_ of layers, its band "cuts" the lifetime of its' children and, if some repeat mode is set, resets their time to 0 for every repetition (or just hides them, if not)
- If this collection is a _Group_ (formerly Clip) _and some repeat mode is set_, its band do not cuts the lifetime of its' children (they continue to move and progress without resetting the time, even if the band is finished), but rather cuts the lifetime for its' tweens, so tweens altogether are starting at 0 for every repetition

May be it needs a more beautiful way to implement this. I'll think on this.
Some food for thoughts: http://programmers.stackexchange.com/questions/125320/do-todo-comments-make-sense, http://c2.com/cgi/wiki?TodoCommentsConsideredHarmful.

Wunderlist/Checkvist/Whatever also do not sticks to the exact line of code, and usually it is important for TODOs—when I have the code around I usually get why I left this short TODO comment here (instead of a lot of a text in a task).

On the other hand, I probably like [this approach](http://stevenschwenke.de/howIDealWithTODOCommentsInCode): 
> While developing, I try to commit into version control as often as possible. Before the final commit of a feature, I do a full text search in the whole code base to find “my” TODOs and fix them. My goal here is to never commit TODOs permanently.