stackMoveToFinal iterates over finalItems, not currentItems

This makes it possible, to filter items, while building up the
finalItems array. (most other loops are already constructed alike)
Timeline-constructor allows inheritation

When no container is supplied, the timeline constructor simply exits, so
that no runtime error is triggered, and inheritation by
"MyClass.prototype = new links.Timeline(null);" is possible.
Fixed bug in stackMoveOneStep loop

It was iterating over currentItems, but using the index for lookup in
the finalItems-Array
Merge pull request #78 from gagabla/master

Allow extension of links.Timeline using inheritation