static/index.html: Call the initial newmode() after image is loaded, otherwise render() throws an error
static/index.html: +semicolon at console.log() for extra code aesthetics
static/index.html: Change UV plane coordinates by mouse dragging and reduce needless texture transfers + texture VRAM leaks
static/index.html: Promote lenslets to a global variable
static/index.html: Limit the viewing angle by optical system parameters
static/index.html: newmode() does not imply render() anymore - this allows for cleaner main() code
static/index.html main(), newmain(): Factor out a new loadimage() function
static/index.html: Load optics, lenslets from a JSON file at the server side

Example files corresponding to cell_layer_pawel_green_2.tif are provided.
static/index.html loadimage_onload() -> render_if_ready() (to be called from elsewhere too)
static/index.html: Add support for gamma + gain changes
static/index.html: Convert lenslets offset to a corner-based value

Traditionally (even in LFDisplay, but not always as generated by auto-rectify),
the lenslets.offset value is at the center of the image, with lenslets grid
coordinates then being in the [-0.5,+0.5] range. To remove the auto-rectify
related troubles and make the code more natural, we convert the offset value
to one based on the [0,0] image corner coordinates.

Our code to move to the corner is not 100% fool-proof but it should be
Good Enough (tm) for now.
static/index.html render(): Allow alpha-blending during rendering
static/index.html: Add support for rendering the lenslets grid
rawimage-lenslets.json: Adjust the rectification manually a little for the green image
static/index.html: Prettier, more compact controls
static/index.html: Simplify coordinate system handling

Beforehand, the texture loaded from the image was flipped in the Y axis;
to compensate for this, multiple unholy coordinate flips were done, let's
eschew that.
static/index.html lightfield shader: Proper rendering by fixing matrix multiplication order
static/index.html: Keep ofs_{U,V} in the OpenGL coordinate system too
static/index.html: Trigger finer motion by mouse dragging
static/index.html: Show U,V values in the control panel