Current observer used with ranged loop is using massive amount of
memory because each range is generating separate set of bloom filters.
Each bloom filter can be up to 2MB of memory. That's a lot.
This change is initial change to reduce used memory by sharing bloom
filters between ranges and just synchronize access to them. This
implementation is rather simple and even naive but maybe it will be
enough without doing something more complex.
https://github.com/storj/storj/issues/5803
Change-Id: Ie62d19276aa9023076b1c97f712b788bce963cbe
98562d06c8