Switching from inheritance to composition
for datum input modes
Only draw ExpressionFunctionDatums without connections
Fix bad representation of strings
Distinguish between datums that call eval and datums that call a function in parent node
Deflate function datums properly
Removed debugging load stage
Controls should only store references to Node objects, getting controls lazily when needed
Refer to parent node in child constructor
Construct with correct parent
Merge branch 'datum-refactor'
Refactor datum class hierarchy and input system;
Save/load is now working as well.