Fixes to make dijkstra algorithm find canonical shortest path

ref #71
Refactoring DatabaseGraph to allow for pluggable parts

close #72
Highway hierarchies graph, with some more refactoring DatabaseGraph

ref #71
ref #72
Some work on finding highway edges

ref #71
A test for first and second phase of highway hierarchies

ref #71
More work on #71
Work on contraction for hh

ref #71
Tests for tree contraction for hh

ref #71
Initial version of HHStep

ref #71
Refactoring of first and second phases of hh

ref #71
close #48
FIx compilation error
Added highway hierarchies creating command

ref #71
HHStepExecutor

ref #71
Better area cost to cover determining

close #73
Added option to PreciseAreaVisualizer to allow drawing only lines

close #74
Fixed drawing by finding the union of covered areas neighbouring on not completely covered areas. Then removing the holes of the resulting polygons and calling that the covered
area.

ref #75
Trying to fix a problem when the covered polygon could hide some valid holes in the isochrone

close #75
NPE fix and test update

close #75
Added preload-all option to graph operations which allow for preloading the whole graph

close #76
Implemented mavericks for hh

ref #71