Add option to run graphs 'fast'

[m-fila]

Having the algorithms run for a time described in a graph is great, but sometimes it's cumbersome to wait for the completion. For instance, unit testes should be possibly fast and waiting for executing all the algorithms might take some time.
It might be useful to add an option (maybe in MockupAlgorithm constructor?) to override the runtimes provided in graphml with 0 s or some other small value
This option could be also used as another argument for #27