Add term reference tree module.
Merge pull request #5909 from openscholar/5908

Add term reference tree module.
Add term reference tree patch to allow it to work with entity reference module.
Restore make file.
Merge pull request #5916 from openscholar/5915

Restore make file.
Fix notice on vocabulary save.
Revert "Fix notice on vocabulary save."

This reverts commit 838ef6c9dde1a64e601449a45fa0fa0dd88b7d3d.
Merge branch 'SCHOLAR-3.x' into 5894