Feature/Implement connectivity map

[CodeBear801]

Issue

#238

• Implements connectivity map, it builds connectivity for each place point by:
  • find all near by places by spatial index(implements in indexer)
  • ranking near by places by great circle distance or shortest path distance(by osrm)
• Implements a work-poo based builder to do building related tasks, because for each place, if we are using 'OSRM' to calculate shortest path, we need to separate calculation into different workers. OSRM part's logic already be wrapped in osrmconnector, for each worker, when handling a place, he just need submit a http task to osrmconnector and then get a future like channel. The maximum request in osrmconnector equals to NumOfTasks defined here.

/*
                                    ->   tasksChannel   ---> worker
                                  /                                   \
                                 /                                     \
Input Iterator ==> dispatcher    --->    tasksChannel   ---> worker      ---> aggregatorChannel -> iterate and put result to map
                                 \                                     /
                                  \                                   /
                                    ->   tasksChannel   ---> worker
*/

• Add comments for functions(related with code review in Feature/Implement ranker for handling near by points/places #258)

Tasklist

• implement logic
• add tests
• review