Allows for injection of the app object into the request object through
the request handler.
This allows for users to setup things like database connections etc. in
listeners and then utilize them throughout the their various route
handlers.
Usage is fairly simple like so:
```python
@app.get('/')
async def handler(request):
request.app.anything
```
Name is up in the air but I'll leave this up for a few days and I'll
change it if we get a consensus
Functionality wise this won't change much for most users, unless you
were directly importing from `sanic.sanic` in which case I am sorry if
you're affected by this.
Main motivation was because jedi autocompletion didn't work with this
and we were using relative imports to compensate for the fact that
having a module inside of your module with the same name creates major
namespace problems.
