Fixed compiler warning in RiemannSolver.

Eliminate a couple of unnecessary calls to Vmath::Zero.
Fix a couple of compiler warnings.

Changed flux vector so that solver computes all components simultaneously.
Removing some temporary storage from AdvectionFR.
Riemann solvers now store gamma parameter statically.

Conflicts:
	library/LocalRegions/HexExp.cpp

Substitution of Riemann ExactSolver with Riemann ExactToroSolver. Modification of regression test accordingely.

Tidied up 2D MultiplyByQuadratureMetric calls.

Removed code duplication in MultiplyByQuadratureMetric routine.