Replace iostream and fstream includes by iosfwd in OTB headers

Summary

Replace #include <iostream> and #include <fstream> by #include <iosfwd> to reduce building time

Part of #1649 (closed)

Rationale

See #1649 (closed)

Implementation Details

A bit of refactoring was needed in old IO classes, that where using iostream and fstream as class members.

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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