base: wsgi middlewares reorganization

**Problems**
I'm serving invenio using uWSGI:
```console
$ uwsgi --master --processes 4 --die-on-term --http 0.0.0.0:4000 --wsgi-file invenio/invenio.wsgi
AttributeError: 'DebuggedApplication' object has no attribute 'wsgi_app'
...
assert self.script_name == environ['SCRIPT_NAME']
AssertionError
```
**Changes**
* Fixing DebbugedApplication middleware usage. ([_why uWSGI requires it_](http://stackoverflow.com/a/17839750))
* Using an Apache environment variable (`WSGI_SCRIPT_ALIAS`) to detect when to apply the `WSGIScriptAliasFix`.
* **NOTE** <span style="color:#f00">regenerate your apache configuration</span>.

**Notes**
* `%{ENV:WSGI_SCRIPT_ALIAS}` doesn't work(?)
* the Apache environment can only be accessed at `__call__` time.

Related to: #254