[milo] Refactor all html knowledge out of backends.

milo/frontend/view_config.go

Index: milo/frontend/view_config.go
diff --git a/milo/frontend/config.go b/milo/frontend/view_config.go
similarity index 90%
rename from milo/frontend/config.go
rename to milo/frontend/view_config.go
index 1a0c3a0417031dcd299e8bca0c24e3456eb0c435..fe6c391b44695bf31fb208d9cb353420965e50c6 100644
--- a/milo/frontend/config.go
+++ b/milo/frontend/view_config.go
@@ -20,6 +20,7 @@ import (
 	"cloud.google.com/go/datastore"
 	"google.golang.org/appengine"
 
+	"github.com/luci/luci-go/common/errors"
 	"github.com/luci/luci-go/common/logging"
 	"github.com/luci/luci-go/milo/common"
 	"github.com/luci/luci-go/server/router"
@@ -30,16 +31,12 @@ import (
 func ConfigsHandler(c *router.Context) {
 	projects, err := common.GetAllProjects(c.Context)
 	if err != nil {
-		common.ErrorPage(
-			c, http.StatusInternalServerError,
-			"Error while getting projects: "+err.Error())
+		ErrorHandler(c, errors.Annotate(err, "Error while getting projects").Err())
 		return
 	}
 	sc, err := common.GetCurrentServiceConfig(c.Context)
 	if err != nil && err != datastore.ErrNoSuchEntity {
-		common.ErrorPage(
-			c, http.StatusInternalServerError,
-			"Error while getting service config: "+err.Error())
+		ErrorHandler(c, errors.Annotate(err, "Error while getting service config").Err())
 		return
 	}