Standarize inputs as pd.Dataframe / pd.Series

[angela97lin]

Fixes #61

[codecov]

Codecov Report

Merging #130 into master will increase coverage by 0.24%.
The diff coverage is 98.11%.

@@            Coverage Diff             @@
##           master     #130      +/-   ##
==========================================
+ Coverage    96.9%   97.15%   +0.24%     
==========================================
  Files          92       92              
  Lines        2422     2459      +37     
==========================================
+ Hits         2347     2389      +42     
+ Misses         75       70       -5

Impacted Files	Coverage Δ
evalml/__init__.py	100% <ø> (ø)	⬆️
...valml/tests/preprocessing_tests/test_split_data.py	100% <ø> (ø)	⬆️
evalml/tests/objective_tests/test_objectives.py	100% <ø> (ø)	⬆️
evalml/tests/pipeline_tests/test_pipelines.py	100% <ø> (ø)	⬆️
evalml/tests/objective_tests/test_lead_scoring.py	100% <100%> (ø)	⬆️
evalml/objectives/fraud_cost.py	100% <100%> (ø)	⬆️
...alml/tests/objective_tests/test_fraud_detection.py	100% <100%> (ø)	⬆️
evalml/pipelines/pipeline_base.py	95.58% <100%> (+0.2%)	⬆️
evalml/preprocessing/utils.py	83.72% <100%> (+1.66%)	⬆️
evalml/objectives/lead_scoring.py	96.66% <85.71%> (-3.34%)	⬇️
... and 1 more

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[jeremyliweishih]

LGTM other than these test additions.

[jeremyliweishih]

LGTM. Lets just wait for ci to report.

[kmax12]

this looks good to me. although, as i was going through i noticed we aren't consistent with how we output stuff as pandas vs numpy. opened #236 to work through that

[kmax12]

LGTM