Added a feature flag for impala browse pages.

Set IMPALA_BROWSE = True to re-enable them on a given environment.

apps/addons/templates/addons/impala/home.html

@@ -23,7 +23,7 @@
 <!-- aww yeah -->
 
 <section class="secondary">
-  {{ side_nav(amo.ADDON_EXTENSION, impala=True) }}
+  {{ side_nav(amo.ADDON_EXTENSION, impala=settings.IMPALA_BROWSE) }}
 </section>
 
 <section class="primary" id="homepage">

settings.py

@@ -945,6 +945,7 @@ UNLINK_SITE_STATS = True
 
 # Use the new featured add-ons system which makes use of featured collections.
 NEW_FEATURES = False
+IMPALA_BROWSE = False
 
 # Set to True if we're allowed to use X-SENDFILE.
 XSENDFILE = True