Point cloud Picking texture splat size and circle selection

[chemseddinehimeur]

Hello,

Using the picking feature on radium is very difficult because the splat size doesn't change with point cloud splat size, and initial size is often too small to use with sparse point clouds.

Circle selection makes the picking even harder, because for some reason it's not possible to select surrounding points unless the mouse pointer is exactly on a picking splat. If the mouse pointer is not on a picking splat, the circle select fails to register any of the points inside the circle. Combine that with sparse/small picking splats and it becomes virtually impossible to select points on some point clouds.

[nmellado]

Hacked in #840, we can keep it open as a reminder