Modify functions called on key events

Call disconnect nodes function if a connection is selected, else call delete nodes.
Clear current selected nodes name list when a connection is selected
Clear current selected nodes name list when clicking on the background
Use Connections to update the text color of the current selected node
Modify setCurrentSelectedNodes function so it takes a list of nodes instead of a single node

Add a slot appentToCurrentSelectedNodes
Add slot disconnect() in buttleManager
Merge branch 'develop' of github.com:buttleofx/ButtleOFX into develop

Conflicts:
	buttleofx/MainWindow.qml
	buttleofx/gui/graph/qml/Tools.qml