convert gl3 to gles (to allow the usage for the emscripten backend)

[mgerhardy]

ERROR: 0:1: '130' : client/version number not supported caveexpress.html:1:1650
ERROR: 0:3: 'in' : storage qualifier supported in GLSL ES 3.00 and above only caveexpress.html:1:1650
ERROR: 0:4: 'in' : storage qualifier supported in GLSL ES 3.00 and above only caveexpress.html:1:1650
ERROR: 0:5: 'in' : storage qualifier supported in GLSL ES 3.00 and above only caveexpress.html:1:1650
ERROR: 0:9: 'out' : storage qualifier supported in GLSL ES 3.00 and above only
ERROR: 0:10: 'out' : storage qualifier supported in GLSL ES 3.00 and above only