Algorithm database sharing

Closes #103

See merge request !128

beat/beat.cmdline re-implements similar parts so
make them reusable

This will grab the version currently used for the test
and in this case with the root_folder entry fixed for
the tests.

This will allow to use them in the same temporary
folder used for other test data.

It's not handled in the setup/teardown of the test package.

This will avoid the docker daemon to create them
and make them belong to it and thus not properly
accessible if the daemon is root.

This will allow the docker tests to more easily setup and
cleanup its content.

While the folder is not used as these databases are generative
only, docker will create it anyway as mounting a non-exisiting
folder will trigger its creation with the daemon ownership
applied.

A new property in the execution configuration allows to
mount the various databases in the algorithm container
in a similar fashion as the database container. It will
only work for containers that needs to access datasets.

Fixes #103

Update docker related information

See merge request !127

The links to the images have been updated to use docker hub and there's
also a new paragraph about beat/beat.env.example>.

Pre commit cleanup

See merge request !126

Add minimal rw tmpfs for /tmp and /run

Closes #101

See merge request !125

At least in production, some issues happened that required
to have /tmp writable. To preserve the read-only state
of the container, use a small tmpfs that is enough for
the container to run. /run is another that might be needed
so make it part of the defaults used.

Add test for setup in cxx algorithm

See merge request !124

This test ensures that the setup feature works properly.

Ensure that writing to a non existing output shows an error

See merge request !123

It has been the case for a while for beat/beat.backend.cxx>

- beat.env.python.tests 1.3.0r7
- beat.env.db.examples 1.4.0r7
- beat.env.cxx 2.0.0r4
- beat.env.cxxdev 2.0.0r4

Add optionnal environment entry to database

See merge request !122