Graph_directed second commit.
Added:
- mouse over existing vertex --> draw edge between those vertices (not creating new one)
- fix minor bugs
- edge weight (not rotated, 3 quater, right side).
- reuse lowest no that is available when creating new
- alt + click and drag -> move vertex + assoc edges
- click + drag -> new edge
- click + drag into existed vertex -> connect to existed vertex
- skeleton of the tables

TODO:
- edge weight: currently it's just "for demonstrating" i.e not attached to the edge. When the edge is deleted it's not deleted, when the edge is moved it's not moved. Finish this.
- complete populating tables
- is bipartite, is complete
- UI for switching between direct/indirect/advanced
- fix minor bugs if found