Initial pass at radial scrolling
Add missing iOS shaders and files for radial scrolling
Clarify error reporting when loading shaders.
In which we use conditional compilation to avoid maintaining platform-specific GLSL shaders.
Fix a crash when leaving then entering foreground on iOS.
Use VAO util in column shader.
Save radial scrolling work - probably not going to use as it doesn't look that good
Minor updates to radial scrolling
Use the same shader for all scrolling renderers
Unify remaining shaders
Default back to linear scrolling
Adjust intervals on Mac (needs looking at again)