Fix json and xml views breaked by wrap view of developer tools

When developers wrap view option is activated, that's break all json and xml output.
Json data is wrapped by `<!-- developers:begin myview -->{"myjson":"mydata"}<!-- developers:end myview -->`.

**I tried this cases :**

- with my view in myplugin/views/default/myplugin/myview.php and an elgg_register_ajax_view for this view.
 -> view is breaked with wrap view option.
- with my view in myplugin/views/json/myplugin/myview.php and an elgg_register_ajax_view for this view.
 -> view is breaked with wrap view option.

I looked inside elgg core and I think best practice is :
- register view with elgg_register_ajax_view that return json,
- put this view in myplugin/views/json/myplugin/myview.php
- call this view with elgg.post or elgg.get with view: 'json' as parameters

So, for this case, we should add json parameters in $excluded_bases.

Everythings is same with xml output.

I wish I get the right way to get json ouput and wrap view activated.