Right now we have a problem in that the important scale factors of 1.25 and 1.75 are
not reachable using the UI. However just reducing the slider increment to 0.05 would
result in way too many slider values. Instead, this patch implements the following:
- Slider goes by increments of 0.25
- The user can show an advanced scaling settings dialog that exposes a UI to set the scale factor with increments of 0.05
This way the commonly-used scale factors are more accessible, but more granular values
are made available to people who really need them and are likely to go poking around.