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Some cleanup changes suggested by rmpowell and noahsark
Changed clipboard format name for sheet
changing const data style from macro to static object, making it a specific type.
changing add sheet to go through field-view, which will enable do/undo actions.
Now using an std::unique_ptr
Merge branch 'CopyPasteSheet' of http://github.com/calband/calchart into CopyPasteSheet

Conflicts:
	src/field_frame.cpp
Update field_frame.cpp

merging lines into 1 step (release() acts like get())
Merge pull request #81 from calband/CopyPasteSheet

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