Limit graph search/crash when there is no connection

[NopMap]

Implement an upper bound to the weight of partial solutions examined by the search algorithms. Solutions exceeding the upper bound are not expanded but discarded. Search is thus limited to a reasonable range.

The cutoff value is the longest acceptable detour for a vehicle multiplied with the worst possible weight assigned to an edge plus some tolerance.

[NopMap]

Implementation complete locally for AStar and AStarBidirection. Cutoff will have to be adjusted according to use case. In my test case it is 100 times the direct distance between the points. This is a fairly safe value but in my test case reduces the calculation time from 38s to 4s.

I was unable to merge the EdgeExplorer changes from master to my branch, so I will make a pull request once I'm back on the master.