According to /incoming specification, this parameter doesn't exists. It
was added on MX side and brought here on transition. This commit
explicitly removes it, leaving a track on history that it got removed
during transition. Further work on MX will also remove the "NONE"
encryption scheme, which is part of dead code.

Use the same formatting as MX was using for backwards compatibility.

-- Resolves: #8828

-- Resolves: #8827

That's the resource used for incoming documents or documents to be added
externally into user's db.
- Related: #8827

We have been discussing about this merge for a while.
Its main goal is to simplify things: code navigation, but also
packaging.

The rationale is that the code is more cohesive in this way, and there's
only one source package to install.

Dependencies that are only for the server or the client will not be
installed by default, and they are expected to be provided by the
environment. There are setuptools extras defined for the client and the
server.

Debianization is still expected to split the single source package into
3 binaries.

Another avantage is that the documentation can now install a single
package with a single step, and therefore include the docstrings into
the generated docs.

- Resolves: #8896

- Resolves: #8804

- rename add_tag method
- reorder blob interface methods for clarity
- use mkdir_p from leap.common