Hide nodes that are not "unlocked" about acas

[dwp7kp]

Branch:
gradeDisplay

Currently:
System only shows nodes that are at competency or higher and their immediate leaves.

Todo:
I don't think it will enforce multiple parent nodes

Issues:
If we plan to allow automatic grading for CS courses, it's possible a student could have a prior node at competency and then fail it (with a null pointer error or something). This would re-lock farther nodes and mess up drawing the tree. Example below.

Full tree view

Student view if they had passed graphs, a star, and fourth topic and later fail a star.

This happens because node 'fourth topic' is still technically passing. What should we do about this?

[dwp7kp]

Branch:
gradeDisplay

Currently:
System only shows nodes that are at competency or higher and their immediate leaves. Enforces passing all parent nodes.

Todo:
Resolve issue of later failing a prerequisite node.

Issues
Graph gets tangled if topics are complicated. Try to prevent crossing lines. Example:

[dwp7kp]

We decided the graph would no longer hide locked nodes. Tree breaking is no longer an issue because all nodes are always present. Moving graph edge crossing to a new issue.