model.optimize selects a qp enabled solver
model.optimize selects a qp enabled solver

When no solver is specified and a quadratic component is given, cobrapy
will now correctly use a solver which supports quadaratic programming,
as determined by the presence of a set_quadratic_objective function.

This fixes #109.

zakandrewking/cobrapy,aebrahim/cobrapy,zakandrewking/cobrapy,jerkos/cobrapy,aebrahim/cobrapy,jeicher/cobrapy,jerkos/cobrapy,JuBra/cobrapy,jeicher/cobrapy,JuBra/cobrapy