Convert Tree to mixin and update tests

* Move various methods from column definition to instance
* Refactor aspects into prototype method extensions
Fix to the top heavy manual tree test.
Simplify the hierarchical tree stores

Add manual and automated tests to demonstrate how to do additional
filtering of children on a hierarchical store.
Tree: move collapseOnRefresh to instance-level and remove tree property

column.renderExpando will serve tree property's purpose; true = use default
tree: Add enableTreeTransitions flag, and clean up _calcRowHeight
Update Tree documentation
Update tests from tree plug-in to Tree mixin.
Further updates to Tree documentation
Tree: Minor formatting/comment/naming tweaks
Tree tests: minor efficiency improvements