Grease Pencil already implements support for full-featured per-brush pressure curves, but it is useful to have some basic global settings that affect all brushes and tools. This adds two simple options: - Raw pressure required to achieve full brush intensity. - Softness control, using a gamma curve internally. The most important one is the max pressure setting, because it is critical for ergonomics, but the Linux Wacom driver lacks it. The softness option internally converts to gamma = 4^-softness. Reviewers: brecht, campbellbarton Differential Revision: https://developer.blender.org/D3967