Correct decorator implementation using the wrapt library

[sphuber]

Fixes #2446

The naive implementation of a decorator will break some of the
functionality of the functions they wrap. For example, the original
docstring will be lost. The module functools provides the wraps
decorator to fix this problem, but this is not the only issue. In
addition to the docstring, other properties, such as the function
signature are also lost. This means that using the inspect module on
decorated functions is hopelessly broken. The wrapt library provides
the decorator decorator that simplifies writing decorators, while
ensuring that all the important properties of wrapped function are
maintained.

[sphuber]

A few notes:

1. I have not adapted the implementation of the protected nor override decorators yet because they are a bit more complicated.
2. The same goes for the calcfunction and workfunction decorator
3. The with_dbenv currently does not take an argument, so could be simplified by removing a wrapping layer. However, this will require it to be used as @with_dbenv instead of @with_dbenv(). Since this is a breaking change, I have left it. Moreover, if in the future we want to allow to specify which profile to load through the decorator, this can be done without breaking the interface, I think

Before I try to see if I can tackle 1 and 2, I wanted to see if you guys feel this is worth the added dependency. I certainly do in any case.

[coveralls]

Coverage increased (+0.05%) to 73.217% when pulling b28642a on sphuber:fix_2446_wrapt_decorators into 9abc4ff on aiidateam:develop.

[ltalirz]

wrapt seems like a nice library, and it's available on conda as well.
the only criticism I could have here is that it seems to have a bus factor of 1 and that I don't consider the features we add here terribly important - I agree that they are nice to have, though, and would be ok with including wrapt as a dependency.

[giovannipizzi]

Same comment as @ltalirz - anyway it seems that the library is quite stable and only doing bugfixes in the past two years.

[ltalirz]

fine to go ahead!