Add parameter to load a single graph direction in memory.
Currently, the server loads both the forward and the transposed graphs into memory.
Added direction
server option to specify which graph directions should be loaded into memory (forward|backward|both)
defaulting to both
of not provided.
If a single direction was loaded, the direction in the query defaults to the loaded one.
If the user queries the direction, that was not loaded, the server response reflects that.
Migrated from D6594 (view on Phabricator)