Set collapse_navigation to true (#600)

This matches 0.2.4 behavior. Although it might not be desired behavior, the behavior of setting this to true can result in file size to explode and build times also.

This was caused by bf9faa98f0 which effectly switched the logic of `collapse_navigation`

sphinx_rtd_theme/theme.conf

@@ -6,7 +6,7 @@ pygments_style = default
 [options]
 canonical_url =
 analytics_id =
-collapse_navigation = False
+collapse_navigation = True
 sticky_navigation = True
 navigation_depth = 4
 includehidden = True