all: Remove lib/util package (#9049)

Grab-bag packages are nasty, this cleans it up a little by splitting it
into topical packages sempahore, netutil, stringutil, structutil.

lib/stringutil/stringutil.go

@@ -0,0 +1,46 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package stringutil
+
+import (
+	"strings"
+	"time"
+)
+
+// UniqueTrimmedStrings returns a list of all unique strings in ss,
+// in the order in which they first appear in ss, after trimming away
+// leading and trailing spaces.
+func UniqueTrimmedStrings(ss []string) []string {
+	m := make(map[string]struct{}, len(ss))
+	us := make([]string, 0, len(ss))
+	for _, v := range ss {
+		v = strings.Trim(v, " ")
+		if _, ok := m[v]; ok {
+			continue
+		}
+		m[v] = struct{}{}
+		us = append(us, v)
+	}
+
+	return us
+}
+
+func NiceDurationString(d time.Duration) string {
+	switch {
+	case d > 24*time.Hour:
+		d = d.Round(time.Hour)
+	case d > time.Hour:
+		d = d.Round(time.Minute)
+	case d > time.Minute:
+		d = d.Round(time.Second)
+	case d > time.Second:
+		d = d.Round(time.Millisecond)
+	case d > time.Millisecond:
+		d = d.Round(time.Microsecond)
+	}
+	return d.String()
+}