Fixed bug in list layout, which caused the size of the list to become zero when there was only one node in the list. The size of an empty list is now the size of one (empty) node.
Fixed issue with binary tree, where a null node could overlap another node.
Brought back finder as a grader, and fixed the way total steps were counted.
Fixed undo for finder grader
Merge pull request #121 from X455u/listlayout

Fixed bug in list layout
Merge pull request #123 from X455u/treefix

thanks!
Merge pull request #124 from X455u/findgrader

Grader: finder