add Rgputools easyconfigs

Hi,
this one looks surprisingly simple but it proved to be very tedious business (spin-off of #282); reason is you MUST:
1) untar/retar manually the tarball coming from github (reason: incompatibility github vs R-untar, see eb/#313 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 down 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>