static/index.html pinhole fragment shader: There is no gl_Color in WebGL
static/index.html pinhole fragment shader: Split out u_UVCoord from v_texCoord, abolish u_RTM and xyuv
static/index.html render_lightfield_pinhole(): An alternative to render_image()

Quick'n'dirty version with hardcoded lenslet parameters. These come from
cell_lenslets.txt, tested on cell_layer_pawel_green_2.tif.
static/index.html pinhole fragment shader: Remove a useless if condition
static/index.html: Add support for switching between image and light field views
static/index.html: Show an error message in case WebGL is unavailable