Added support for positions relative to _ARRAY_ in graph_copy_with_names. Relative positions are used for systems with address space layout randomization systems (e.g. MacOS).

Added graph_copy_with_names and symbols_in_program from SVN (https://svn.cs.ru.nl/repos/clean-libraries/trunk/Libraries/graph_copy/)

Updated copy_graph_to_string.c with version from SVN (https://svn.cs.ru.nl/repos/clean-libraries/trunk/Libraries/graph_copy/)

Moved copy_graph_to_string.c and copy_string_to_graph.c to common because they are equal for all the platforms.

Initial commit graph-copy files from iTasks-SDK repository at commit 71b3c92c (https://gitlab.science.ru.nl/clean-and-itasks/iTasks-SDK/tree/71b3c92ca46ab50ed4131edddbd9318be34e79fb/Dependencies/graph_copy).