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

this commit deliberately *duplicates* the dependency information between
the setup.py and requirements.pip.

The rationale behind it is that one of them is the generic dependency
information, to be passed to system helpers in order to package it.

The requirements.pip has any pinning information that we want to impose
during development, and it behaves as a well-known set.

Read https://caremad.io/posts/2013/07/setup-vs-requirement/ for more
explanations.

- Resolves: #8830

At this point tests are not yet collectable
in the new environment. But no regressions observed.

Our magic value wasn't being used and were represented as a string.
Refactored it to a constant, increased it's size to 2 bytes and optimzed
is_symmetrically_encrypted to look for the magic and symmetrically
encrypted flag under base64 encoding. Most file types will use this
feature to help identifying themselves, so it got refactored to serve
the purpose it was created.

Those are already present, but we are using the ones coming from our
dependencies. Explicit is better than implicit.