Make it possible to add a component in middle of existing connection #79

Often you want to modify data that is passing through a connection. For this, it should be possible to add a new node there.

• Select an edge
• Click "add" button in edge menubar
• Component list pops up listing only components that are compatible with the data passing through
• On selecting a component the edge is removed, a new node is added to the middle of it, and connections made to connect it to both sides of the original edge