Create lightweight forks of text/template and html/template

This commit also removes support for Ace and Amber templates.

Updates #6594

tpl/strings/strings.go

@@ -18,6 +18,7 @@ import (
 	"errors"
 	"fmt"
 	"html/template"
+
 	_strings "strings"
 	"unicode/utf8"
 

tpl/strings/strings_test.go

@@ -15,6 +15,7 @@ package strings
 
 import (
 	"html/template"
+
 	"testing"
 
 	qt "github.com/frankban/quicktest"

tpl/strings/truncate.go

@@ -17,6 +17,7 @@ import (
 	"errors"
 	"html"
 	"html/template"
+
 	"regexp"
 	"unicode"
 	"unicode/utf8"

tpl/strings/truncate_test.go

@@ -15,6 +15,7 @@ package strings
 
 import (
 	"html/template"
+
 	"reflect"
 	"strings"
 	"testing"