Temporarily modify width and feather during Quick Sizing

[khoidauminh]

During Quick Sizing, Pencil2d tries to write changes to disk every time the width/feather changes. Some devices, particularly drawing tablets, send events at a high rate, causing Pencil2d to fail to keep up with with the events and hang for a moment.

This PR temporarily fixes the issue by introducing new methods that only changes the properties, then calling the original methods (which includes writing to disk) once we're done doing Quick Sizing.