Add a single call function for nonlinear problems

[frapac]

Original idea: jump-dev/MathOptInterface.jl#846 (comment)

We should be able to specify a nonlinear problem quickly, simply as

model = MOI.nlpmodel(f, g!, h!,p, x_lb, x_ub, c_lb, c_ub)

and then build the corresponding MOI problem.

Questions:

• Could we specify the linear/quadratic structures apart, using MatrixOptInterface.jl?

[matbesancon]

Should there also be an interface for joint calls returning a tuple (primal-value, gradient). This can be useful for instance when the objective is a large finite sum