Add support for ObjectiveFunction{ScalarQuadraticFunction}

[odow]

Closes #273

[codecov]

Codecov Report

Patch coverage: 96.29% and project coverage change: +0.15 🎉

Comparison is base (ae9186d) 90.71% compared to head (5f53359) 90.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #276      +/-   ##
==========================================
+ Coverage   90.71%   90.86%   +0.15%     
==========================================
  Files           8        8              
  Lines         420      438      +18     
==========================================
+ Hits          381      398      +17     
- Misses         39       40       +1     

Impacted Files	Coverage Δ
src/MOI_wrapper/MOI_wrapper.jl	92.08% <96.29%> (+0.11%)	⬆️

... and 1 file with indirect coverage changes

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