Feature/add sqlite handler in optuna csproj

[hrntsm]

Reference Issues/PRs

What does this implement/fix? Explain your changes.

• Add class for handling SQLite in optuna.csproj.

[codecov]

Codecov Report

Attention: 60 lines in your changes are missing coverage. Please review.

Comparison is base (c252fa3) 53.51% compared to head (c841137) 70.54%.
Report is 3 commits behind head on develop.

Files	Patch %	Lines
Optuna/Storage/RDB/Storage.cs	86.52%	52 Missing and 7 partials ⚠️
Optuna/Study/MultiObjective.cs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #244       +/-   ##
============================================
+ Coverage    53.51%   70.54%   +17.03%     
============================================
  Files            7        7               
  Lines          598     1015      +417     
  Branches        51       78       +27     
============================================
+ Hits           320      716      +396     
- Misses         261      275       +14     
- Partials        17       24        +7     

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[codeclimate]

Code Climate has analyzed commit c841137 and detected 21 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	9
Duplication	12

View more on Code Climate.