all: rename package ui to unit

Package ui is now only about units except for the Config.Now method.
Remove Now and rename Config to Converter. Add layout.Config to
replace the old ui.Config.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gesture/gesture.go

@@ -11,13 +11,14 @@ package gesture
 
 import (
 	"math"
+	"time"
 
 	"gioui.org/f32"
 	"gioui.org/internal/fling"
 	"gioui.org/io/event"
 	"gioui.org/io/pointer"
 	"gioui.org/op"
-	"gioui.org/ui"
+	"gioui.org/unit"
 )
 
 // Click detects click gestures in the form
@@ -93,7 +94,7 @@ const (
 	StateFlinging
 )
 
-var touchSlop = ui.Dp(3)
+var touchSlop = unit.Dp(3)
 
 // Add the handler to the operation list to receive click events.
 func (c *Click) Add(ops *op.Ops) {
@@ -156,7 +157,7 @@ func (s *Scroll) Stop() {
 
 // Scroll detects the scrolling distance from the available events and
 // ongoing fling gestures.
-func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
+func (s *Scroll) Scroll(cfg unit.Converter, q event.Queue, t time.Time, axis Axis) int {
 	if s.axis != axis {
 		s.axis = axis
 		return 0
@@ -185,7 +186,7 @@ func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
 			}
 			fling := s.estimator.Estimate()
 			if slop, d := float32(cfg.Px(touchSlop)), fling.Distance; d < -slop || d > slop {
-				s.flinger.Start(cfg, fling.Velocity)
+				s.flinger.Start(cfg, t, fling.Velocity)
 			}
 			fallthrough
 		case pointer.Cancel:
@@ -221,7 +222,7 @@ func (s *Scroll) Scroll(cfg ui.Config, q event.Queue, axis Axis) int {
 			}
 		}
 	}
-	total += s.flinger.Tick(cfg.Now())
+	total += s.flinger.Tick(t)
 	return total
 }