Advanced Blueprint importing interface

This PR is extended from #44.
## Feature
* Integrate blueprint into D configure
* Use one blueprint many times (use deepcopy)

```python
d(
    ....
    mounts={"app2": "/app2/"},
    blueprints={
        "app3": {"blueprint": "app3.views.bp", "url_prefix": "app3/"},
        "app3-clone": {"blueprint": "app3.views.bp", "url_prefix": "app3-clone/"},
    },
    .....
)
```


I was thinking if we can make {"blueprint": "app3.views.bp"} also just "app3.views.bp". Only if you want to use more advanced features you pass a dictionary. 

And some documentation please :-)