CMS-3868 Replace ExtJS grid - TreeGrid must support setting an inital state

Made some renames:
`TreeNode<NODE>` as node or nodes.
`NODE` as data and dataList.
Added `TreeGrid.fetchRoot()` method, that can be overridden. By default
it fetches root data as `TreeNode.fetchChildren()` with an empty
parameter.
ModuleTreeGrid will use and override `fetchRoot()` instead of
`fetchChildren()`. `hasChildren()` will be used in default
implementation and always return false.