Add tree functional tests and more unit tests

Functional tests:

* expand/collapse

Unit tests:

* mayHaveChildren and expando display
* shouldExpand
* renderExpando
* renderCell
Tree test cleanup

* Add tree tests to functional test module
* Remove some duplication for renderExpando test
* Lint/formatting fixes
* Change the dgrid module ids back to absolute rather than relative
* Simplify the createGrid function a bit
* Skip the functional tests in Safari because mouseMoveTo is not supported