Refined map updates for location updates

Made a pathfinding session end when the user gets within 10 seconds of
the location.  Made map markers not popup if they weren't changed by a
filter.  Map markers are now linked to the destination, and
destinations no longer get wiped and re-entered with every call to the
server, instead only new ones are accepted and existing ones are
updated.  Added heading updates to rotate the map when the user
rotates, but I can't test this on my laptop.  Lowered the radius of the
5 min and 10 min circles to more accurately match Midtown, but these
values may need further tweaking.  Added detecting for if you are in
range of a destination (within 10 seconds of walking.)  Tapping on a
marker for a destination you are in range of will say "You Are Here"
instead of "Tap for Directions."  Also updated the table to reflect
this check for "You Are Here".  Destinations within 10 seconds will say
"you are here" while destinations that were previously 0 minutes will
say "less than a minute walk".