Rename Basilisk's webextensions component directory to better reflect what it is. Also, add an Application level configure option to disable webextensions

browser/components/moz.build

@@ -10,7 +10,6 @@ DIRS += [
     'customizableui',
     'dirprovider',
     'downloads',
-    'extensions',
     'feeds',
     'migration',
     'newtab',
@@ -26,6 +25,9 @@ DIRS += [
     'translation',
 ]
 
+if CONFIG['MOZ_WEBEXTENSIONS']:
+    DIRS += ['webextensions']
+
 DIRS += ['build']
 
 XPIDL_SOURCES += [