add code for getting canonical rep, testing centroid calc
tweak getCentroid, modify getCanonicalRep so that it takes in data model, add to tests
add canonicalize to api.py, add canonicalize to documentation
clean up imports, comments in centroid.py
clean up imports in canonicalization testing
Cleaned up some stylistic things.
Merge pull request #260 from datamade/canonical

Canonicalization, closes #18, @cathydeng's first dedupe PR !!!