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

by subclassing the MissingDesignDocError, we don't have to import the
soledad.common.couch submodule into the soledad.client.sync

- Resolves: #7626

README with information about latest change, missing docs and licenses,
variable naming and pep8.

From:
[refactor] removing getters and setters from couch.py
_couch_url was a private variable with getter and setter doing the same
as a public variable. It is accessed all over the code, so being private
with getters and setters didnt make sense. This commit fixes the tests
to also follow this style from now on.