Further unification the solver interface

For common functionality, the goal should be for solvers to behave the same way with the same API.
These parameters should be set with an identical API:
- [x] time_limit
- [x] tolerance_feasibility*
- [x] tolerance_markowitz
- [x] iteration_limit
- [x] quadratic component
- [x] objective_sense
- [ ] method (with defined values for primal, dual, and auto at minimum)
- [ ] verbose (what should this be called?) 

* glpk_solver.py actually uses the tolerance_optimality parameter for this instead. Is this a bug?