make the browser overlay (sync.xul) localized and localizable

services/sync/locales/en-US/sync.dtd

@@ -0,0 +1,6 @@
+<!ENTITY syncMenu.label       "Weave">
+<!ENTITY logInItem.label      "Sign In...">
+<!ENTITY logOutItem.label     "Sign Out">
+<!ENTITY syncNowItem.label    "Sync Now">
+<!ENTITY openPrefsItem.label  "Weave Preferences...">
+<!ENTITY openLogItem.label    "Activity Log...">

services/sync/locales/en-US/sync.properties

@@ -0,0 +1,2 @@
+# %S is the date and time at which the last sync successfully completed
+lastSync.label = Last Update: %S