Made addNext and addPrevious also addPrevious and addNext for the other nodes

To do:
- Testing for those
- Tests for tasks (including the same repciprocity)
- Replacing usage of custom nodes and tasks for these models in the app
Testing for Task and node addition reciprocity.

To do:
- Replacing usage of custom nodes and tasks for these models in the app
Removed empty controller.
Made tests pass temporarily.
Replaced usage of generateNewTask with Task constructor.
Removed bogus code.
d3Service tests
Refactored connectNodes, disconnectNodes outside of sugiyamaService.
Refactored usage of nodes and tasks outside of services. Needs tests.
.toString and tests.
Fixed missing test for sugiyama service.
Refactored taskDependencyService.removeFromDependencies into taskListService.removeTask
Removed taskDependencyService.
Unit test and fixes for detecting suggested tasks.
Added arrows to graph.
Fixed tree size calculation and task marking as suggested.
Fixed calculation direction.
Displaying next to complete tasks in graph.