Add multiple edges simultaneously

[fsoupimenta]

Closes #453
Closes #447

[fsoupimenta]

@GraphFilter/version-3-0

The functionality has been implemented and is available for testing by running the application.
However, I believe that the responsibility for this issue belongs to the netgraph library, and not to us. That's why I took the initiative to open an issue in their repository with this request: paulbrodersen/netgraph#88

In addition, during implementation, i identified some bugs that caused the software to fail. To get around these problems, it was necessary to overwrite the netgraph method of adding nodes. This reinforces the idea that it is not our responsibility to implement this functionality.

Note

While we wait for a response from the netgraph, if you want to test the functionality, simply select several vertices at the same time using Ctrl + left mouse click and drag, then press the plus button + or = anywhere on the board.

[atilaajones]

@fsoupimenta
I did the tests.
I observed some unexpected behavior when running the procedure:

1. Select several vertices using the rectangle with the left mouse button;
2. Insert new vertex;
3. The software slowed down a bit and lost the labels of the new vertices

The same behavior occurred when selecting using the CTRL button. Is this the same behavior you got?

Please note that the issue paulbrodersen/netgraph#88 has been answered, so please forward it.