Simplify linear algebra operations syntax in colgen

[guimarqu]

• data structure to store pre-computed information for the subgradient
• replacing all custom code for linear algebra with a generic one
• restructuring a little bit the MP/solutions.jl file (methods on abstract solution/primal solution/dual solution/linear algebra)

[codecov]

Codecov Report

Merging #712 (661f9ad) into master (5f56232) will decrease coverage by 0.01%.
The diff coverage is 93.79%.

@@            Coverage Diff             @@
##           master     #712      +/-   ##
==========================================
- Coverage   86.27%   86.26%   -0.02%     
==========================================
  Files          58       58              
  Lines        5765     5724      -41     
==========================================
- Hits         4974     4938      -36     
+ Misses        791      786       -5     

Impacted Files	Coverage Δ
src/Coluna.jl	100.00% <ø> (ø)
src/MathProg/vcids.jl	88.57% <0.00%> (-2.86%)	⬇️
src/Algorithm/colgenstabilization.jl	94.73% <83.33%> (-3.03%)	⬇️
src/MathProg/solutions.jl	87.03% <94.64%> (+5.30%)	⬆️
src/Algorithm/colgen.jl	80.72% <95.38%> (+0.98%)	⬆️
src/ColunaBase/solsandbounds.jl	89.82% <100.00%> (ø)

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