add GROMACS v4.6 easyconfigs


highlights:
* 2 versions supplied, one with CUDA, one without
* FFTWsp dependency exists, but not included, since we may opt for an FFT-jumbo build
* easyblock must also be provided later, otherwise there we have no sanity_checks etc.

Ref:
* 1.3.2.1. 3.2.1. Running in parallel: http://www.gromacs.org/Documentation/Installation_Instructions#3.2.1._Running_in_parallel
* 1.3.4.1. 3.4.1. FFTW: http://www.gromacs.org/Documentation/Installation_Instructions#3.4.1._FFTW
(generally the installation instructions are a must-read and things can be tuned more).

fyi. the current initial code is a synthesis of all these bits (reflected in "authors"):
https://github.com/fgeorgatos/easybuild.experimental/tree/master/users/georgets/g/GROMACS
https://github.com/fgeorgatos/easybuild.experimental/tree/master/users/wiktor/GROMACS
https://github.com/fgeorgatos/easybuild.experimental/blob/master/contrib/pkgsrc/20121109/g/gromacs-4.5.5.eb
I took the freedom to add Kenneth, since I know his magic hand will touch this...

Progress is pending now on the FFT/CUDA business.

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>