Switch to framesorter class

[michaelonken]

OverlapUtil:

• Use framesorter class instead of using homegrown sorting.
• Remove the related (then) unused sorting functionality

FrameSorter class:

• Remember frame positions in Result
• Also remember frame positions in sorting result since it is usually
  accessed anyway and interesting for library users that otherwise call
  the underlying method on FGInterface for all frames again.
• The DummySorter does not provide frame positions to keep it as simple
  as possible (i.e. keep it "zero" cost).
• Allow 2^32-1 frames as permitted in in DICOM (i.e. use Uint32 instead
  of Uint16) for frame number index.
• Changed precision from Float32 to Float64 where applicable.
• Added some documentation and some other small changes.