Re-implement node connection creation/deletion slots and node movement signal.

[rayment]

The following slots have been fixed as they were never being called:

• NodeDelegateModel::inputConnectionCreated
• NodeDelegateModel::inputConnectionDeleted
• NodeDelegateModel::outputConnectionCreated
• NodeDelegateModel::outputConnectionDeleted

The following slot has been implemented:

• BasicGraphicsScene::onNodeClicked

The following signal has been fixed as it was never being emitted:

• BasicGraphicsScene::nodeMoved

A nuance concerning nodeMoved, unlike AbstractGraphModel::nodePositionUpdated which is called every frame of movement and captured by BasicGraphicsScene::onNodePositionUpdated, nodeMoved will only be called when the mouse is released, locking the node into its new position. Similarly, onNodeClicked is only called when the mouse is released. See Issue 364 for more information.

Note also that TestFlowScene.cpp is old and no longer works in v3, but does contain some example uses of the fixed slots.

[paceholder]

A general remark: could you please format the code using .clang-format file from the root directory? Or at least fix the indentaion (4 spaces). Thanks

[paceholder]

I fixed the formatting manually and merged

[rayment]

I fixed the formatting manually and merged

Sorry, I've been at work and did not have time to reply. I'll make sure to format it next time.