Add an onLocationChanged hook to objects.

[doughsay]

If an object implements the function onLocationChanged, it will be called anytime the location of that object changes.

[codecov]

Codecov Report

Merging #167 into master will increase coverage by 0.39%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #167      +/-   ##
=========================================
+ Coverage   81.41%   81.8%   +0.39%     
=========================================
  Files          27      27              
  Lines        1673    1682       +9     
  Branches      282     284       +2     
=========================================
+ Hits         1362    1376      +14     
+ Misses        311     306       -5

Impacted Files	Coverage Δ
src/lib/world-object-proxy-builder.js	93.93% <100%> (+0.44%)	⬆️
src/lib/fs-db.js	87.27% <0%> (+3.03%)	⬆️

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