Line handles for moving segments

See attached image. There is no way to move a segment of a line whilst keeping 
the attached nodes still attached.

This is quite well done in Dia, for example.

Original issue reported on code.google.com by charles....@gmail.com on 9 Apr 2014 at 9:56

Attachments:

[Line handles.png](https://storage.googleapis.com/google-code-attachments/evoluspencil/issue-629/comment-0/Line handles.png)

N0R7H / evoluspencil

Line handles for moving segments #629