Add Series.str.title to API

[devin-petersohn]

• Resolves Missing 'title' method in StringMethods object #887
• Add Series.str.title to API

What do these changes do?

Related issue number

• passes flake8 modin
• passes black --check modin
• tests added and passing

[codecov]

Codecov Report

Merging #901 into master will increase coverage by 1.36%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #901      +/-   ##
==========================================
+ Coverage   87.71%   89.07%   +1.36%     
==========================================
  Files          54       54              
  Lines        5737     5740       +3     
==========================================
+ Hits         5032     5113      +81     
+ Misses        705      627      -78

Impacted Files	Coverage Δ
modin/backends/pandas/query_compiler.py	89.68% <100%> (+7.88%)	⬆️
modin/pandas/series.py	93.89% <100%> (+0.14%)	⬆️
modin/engines/base/frame/data.py	93.75% <0%> (+2.4%)	⬆️
modin/backends/pandas/parsers.py	65.07% <0%> (+3.17%)	⬆️
modin/data_management/utils.py	90.62% <0%> (+34.37%)	⬆️
modin/engines/base/frame/axis_partition.py	75.55% <0%> (+42.22%)	⬆️

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