add missing libX dependencies for cairo

{cae}[intel/2016a] GATE 6.2 + GATE 7.1 + GATE 7.2 (REVIEW)

{vis}[intel/2016a] PyOpenGL v3.1.1a1

$LD is set correctly in GATE easyblock, so remove from easyconfig (cfr. https://github.com/hpcugent/easybuild-easyblocks/pull/855)

{lang}[intel-2016a] Python 2.7.11 with libX11 1.6.3 (REVIEW)

add comment on recommended CLHEP version in Geant4 easyconfigs

{vis}[intel/2016a] libXpm v3.5.11(REVIEW)

{vis}[intel-2016a] Tk 8.6.4 with libX11 1.6.3 (REVIEW)

{vis}[intel-2016b] Mesa-11.1.2 (REVIEW)

add easyconfig libXft-2.3.2-intel-2016a-libX11-1.6.3.eb, add easyconfig libXpm-3.5.11-intel-2016a.eb, add easyconfig libXrender-0.9.9-intel-2016a.eb, add easyconfig renderproto-0.11-intel-2016a.eb