Refactoring, added deletion and debug argument.

* Prepended _ to a lot of functions in NodeGrapher, as they were private. 
* Removed getter from Node.
* Added the ability to delete links with CTRL+Right Click.
* Added the ability to delete all links with Delete. If there are no links, all nodes will be deleted.
* Added the ability to test if "debug" is in the arguments when running to program, and then a bunch of default nodes and links will be created.