Contrib Rgputools easyconfigs

Hi,
this one looks surprisingly simple but it proved to be very tedious business (spin-off of #282); reason is you MUST:

first, be careful with the exact git commit ID that corresponds to v0.28, this is not exactly a 1-1 relationship :-P

1) untar/retar manually the github tarball ; reason: incompatibility github vs R-untar, see easyblocks thread:
    https://github.com/hpcugent/easybuild-easyblocks/issues/313
2) you still need to supply full path from within R, eg. `dyn.load("/hello/big/world")`, while R_LIB does get populated
3) you need do this on GPU-equiped node, otherwise you receive an obscure message about missing `libcuda.so.1`
4) `e5cb024` works OK, while next commits (all called v0.28!) break down somewhere along the commit sequence. 
Let's focus on the `e5cb024` case for now, that should be the one to get out working first.
I need your help w. arguing the possible workarounds, I have a specified manual reproducible case at this point.

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
aha!! #1150 has the fix for this ;-) thanks, @pescobar !