Add gurobi support

[jayant91089]

Add gurobi support

Gurobi ([http://www.gurobi.com]) is a popular LP solver. Currently ITCP ises QSopt_ex exact rational solver. Gurobi should provide ability to use floating point arithmetic and solve LPs faster, with a caveat that the solutions may not be exact.

This task requires one to write another piece of software, an interface between GAP and Gurobi, very much on the lines of Qsopt_ex-interface, which needs to be tied to symchm.