Removing undirected_long_range_grid_graph

[constantinpape]

Discussing with @abailoni to get rid of undirectedLongRangeGridGraph because the functionality is almost fully present in undirectedGridGraph. What's still missing:

• https://github.com/constantinpape/nifty/blob/master/src/python/lib/graph/undirected_long_range_grid_graph.cxx#L102
• https://github.com/constantinpape/nifty/blob/master/src/python/lib/graph/undirected_long_range_grid_graph.cxx#L107 (might not be necessary because it's only a reshape?)
• Support for the edge_mask (https://github.com/constantinpape/nifty/blob/master/src/python/lib/graph/undirected_long_range_grid_graph.cxx#L54), this should be implemented via another overload of gridRag...Features which take the mask. Will need a quite change to the sampler (should take the edge coordinate instead of the node coordinate). Also it might be necessary to also pass the mask to the projectEdgeIDs function. Not sure yet.

We could then also remove this https://github.com/constantinpape/nifty/blob/46dd374671ec3d517897a68077c3d49a7096ea33/src/python/module/nifty/graph/__init__.py#L120 and refactor the edge mask functionality somewhere else.

[constantinpape]

Implemented in https://github.com/constantinpape/nifty/commit/2c9755bb1e6ffbd48c56b4c7a7d4d45981baa027 https://github.com/constantinpape/nifty/commit/02197fd7442bfe3897d8dc238c2d653a108d2d34 https://github.com/constantinpape/nifty/commit/83faeb9a5211cf5dcf7e6a6398f0a62ad2059002

Not properly tested yet. @abailoni let me know once you had a chance to test this and if there is anything else we would need to get rid of the long range grid graph. Or if anything is wrong with the implementations.