Many trash objects after deletion workpiece.

[Roman Telezhynskyi]

Workpiece use many modeling objects that also need delete if we don't need them anymore. First it is not so easy since we can't know exactly who also use modeling object. Second gather this information also not easy task. It is not urgent task, but in future will create problems for user. Size of file we continue grows, parsing speed continue slowdown.

[Roman Telezhynskyi]

Resolved by using new Garbage collector and attribute 'inUse'.