[PLAT-6655] Matrix computation for portfolio hedging calculator

Also includes [PLAT-6656] example tests
[PLAT-6656] Examples of portfolio hedging calculation
[PLAT-6655] Tidy up matrix calculator code
Merge branch 'develop' into topic/PLAT-6655
[PLAT-6655] Test corrected
Merge pull request #139 from OpenGamma/topic/PLAT-6655

Topic/plat 6655 - completed.