add password/prompt strings (bug 28792, r=cmanske, sr=hewitt)

editor/ui/composer/locale/en-US/editor.properties

@@ -29,6 +29,8 @@ ExportToText=Export to Text
 EditMode=Edit Mode
 Preview=Preview
 Publish=Publish
+SavePassword=Use Password Manager to save this password
+SaveUsernamePassword=Save username and password
 CorrectSpelling=(correct spelling)
 NoSuggestedWords=(no suggested words)
 NoMisspelledWord=No misspelled words