epsilonWallFunction: Updated to work with both low- and high-Reynolds number turbulence models

This boundary condition provides a turbulence dissipation wall constraint
for low- and high-Reynolds number turbulence models.

The condition can be applied to wall boundaries for which it
- calculates \c epsilon and \c G
- specifies the near-wall epsilon value

where

\vartable
    epsilon | turblence dissipation field
    G       | turblence generation field
\endvartable

The model switches between laminar and turbulent functions based on the
laminar-to-turbulent y+ value derived from kappa and E.

Recent tests have shown that this formulation is more accurate than
the standard high-Reynolds number form for 10 < y+ < 30 with both
standard and continuous wall-functions.

Replaces epsilonLowReWallFunction and should be used for all
low-Reynolds number models for which the epsilonLowReWallFunction BC was
recommended.