Cleanup and add documentation for tags

* Fixed one scenario to work with the default setting
* Fixed one typo in scenario
* Removed unused tags
* Documented the tags currently in use

Change-Id: I14687782857daf79dcd497b934dff99fc45a3997

tests/browser/features/uls_accept_language.feature

@@ -1,4 +1,4 @@
-@ie6-bug  @ie7-bug  @ie8-bug  @ie9-bug @language @sandbox.translatewiki.net
+@language
 Feature: Universal Language Selector Accept-Language
 
   Scenario Outline: Accept-Language