Configuration refactor

- openblas seems to have some problems with our multithreading

since it's common in downstream modules to have a
type alias for the full storageprovider template
I've added a static method that can be called
from that type w/o needing to extract the
stored type again

You'll have to add braces or string() in someplaces that used them.
See test source change.

since it's common in downstream modules to have a
type alias for the full storageprovider template
I've added a static method that can be called
from that type w/o needing to extract the
stored type again

Looking at them again I see no reason why the storage provider should not
be copyable, so I delegated the copy to the individual access providers.
For this I had to drop one ctor, namely:

```
template <class... Args>
explicit StorageProvider(Args&&... args)
```

That one, however, has been giving me problems for a long time now, so I am
quite happy to drop it. Also, I could not find any use of that ctor. If I
am wrong, there is now a factory method to replace this ctor:

```
auto provider = make_storage<T>(ctor, args, for, T);
```

(9a5b616)

this closes #9