advanced setting to "unlock" memory limit

[toloudis]

Use Case

For advanced users with sufficient computer resources, it would be nice to allow loading larger images.

Solution

Add some option to the tweakpane to allow much larger atlas texture size (absolute upper bound is webgl's reported 2d texture size limit). If tweakpane already allows user selection of texture size, maybe we can change it to allow some range of sizes via dropdown as opposed to free choice.

[toloudis]

This also leads to giving a dialog like agave or other viewers that lets users pick the exact resolution level they want, with the dialog populated from the actual image metadata.