Add proper file api endpoint for cxx

See merge request !338

There's currently no serializer for that function as
the update part is done by hand but the base class code
uses the variable.

The current function used works well for the website
but is not well implemented from an API point of view.

This endpoint will replace it when removing the editing
part of beat.web

Related to beat.cmdline#73

Fix analyzer edition

See merge request !337

Following a previous fix, ananlyzers can't have parameters
therefore this patch removes the possiblity to add them
to the declaration.

Add additional validation for environments/queues

See merge request !336

When creating a new experiment, there's an additional check that is done for
the validity of the environments/queues combination selected that is performed
on save.

This currently does not play nice with the API side as it triggers an error 500
which should rather be a validation error. Therefore the check is now done in the
validate method so that this use case is better handled and allows for a correct
error message to be returned.

Also, now if we get an error when creating a new experiment, an APIError is
generated with it.

Update docker tag in user doc

Closes #552

See merge request !335

Activity stream notification for supervision requests

Closes #496

See merge request !334

Fixes #496

Update execution environment

See merge request !333

To keep in sync with the versions used for the tests.

The latest versions are needed because they provide
the required test data/information updates.

The queue setup part uses outdated environements.

Update them all to reflect what is currently
available.

Notify blocked account user of a successful login attempt and re-activation account steps

Closes #551

See merge request !331

Fixes #551

Update dependencies

See merge request !332

- beat.backend.python to 1.7.7

- beat.backend.python to 1.7.7

Improve automatic emails with temporary urls

Closes #550 and #542

See merge request !328