Implement the grammar for setting dependents and subtasks.
Issue an edit query for setting a task's dependency and subtasks.
Fix lints.
Merge pull request #298 from lowjoel/add-subtasks-and-dependendies-editing

Add subtasks and dependendies editing
Modify controller
Merge branch 'master' of https://github.com/cs2103aug2014-w10-1c/main into subtask-api
Separate basic and advanced tests
Fixes #302 If parent is filtered, don't show the child
Fixes #304 GUI