- id maps are not editable
- handle exceptions thrown by the file reader
- texts are always above the edges
- store a default value for all maps, so that edges and nodes created after
adding a new map receive the default value too
- create node on button release, not on click (fixes a few oddities)

 c LEMON max flow problem

 p max 7 9

 n 1 s

 n 7 t

 a 1 2 3

 a 1 3 2

 a 1 4 1

 a 2 5 3

 a 3 5 2

 a 3 7 5

 a 3 6 3

 a 4 6 1

 a 5 7 2

 a 6 7 4