Converting Task to a Tree structure (#11117)

* added support for tree view

* nestedset added to handle tree based structure

* treeview ui added

* removed is_group dependency

* added validation while editing a group-task

* codacy fix

* BOM like filter added

* Added ui-test for treeview-task

erpnext/config/projects.py

@@ -15,6 +15,7 @@ def get_data():
 				{
 					"type": "doctype",
 					"name": "Task",
+					"route": "Tree/Task",
 					"description": _("Project activity / task."),
 				},
 				{