Instead of introducing arbitrary, fixed-length delays between PokeStop visits

Instead of introducing arbitrary, fixed-length delays between PokeStop visits
and before catching Pokemon, I changed the code to make the length of delay
before interacting with a map object a function of that object's distance.
I also changed the movement algorithm so that the bot does not quit after
just one round of PokeStop visits, but continues to explore until none of
the PokeStops visited in the current round of visits have neighboring PokeStops
which are not in the current round of PokeStops and were visited a long enough time
ago to permit visiting them again.  Overall, the bot has about the same rate of success
for farming items from PokeStops, but does so more quickly.  Due to this and the
increased uptime, these changes result in higher XP/hour and pokemon/hour rates.