We want the default stroke width to be represented by a position
close to the center of the stroke width slider, with max value being
eight times the default value (four times for the blur tool) and min
value being 20% of the default value.
To do that slider value (which grows linearly) is raised
to power of 3 (2 for blur) when that value is > 1, and only then
that value becomes a multiplier for default stroke width.
This change also fixes a bug when bottom buttons in the crop screen
were not visible. That happened because ImageEditorBottomBar by default
had its controls hidden (with the intent that they are animated in once
view controller's view is visible). That was a poor design choice on my
end and is fixed in this commit.
