Firt approximation with the Reader and Visitor.
*) Removed the GlobalOptions-IO related func to
another file (Dr. Dobbs article about encapsulation, Scott Meyers).
More to come here-> read TODO doxy in code.

*) Finished GraphVisitor, copied almost from Dot plugin just to see
if it worked. Now, refactoring!!!!.

*) The reader now has its own header/source file separation. When
I know how to build plugins for OSG, I'll change it again to
source-file only.

*) Added a new test, 'visitor' to check the GraphVisitor.
Merge remote-tracking branch 'origin/master' into development
Moved the tests to a folder of its own and added CMake support.
The colors in the file go encoded as #RRGGBB. Otherwise, ogdf won't recognize them.