Click-odoo

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- add support for launching with ``python -m click_odoo``. Fixes 20.
- apply ``--log-level`` to the root logger, so it works more
intuitively by applying to the script too, and not only to the ``odoo``
namespace. *This may change the log output of some scripts*.
In particular, ``--log-level=debug`` will now apply debug logging
to every python library used, and not only to Odoo.
Fine tuning is available through the ``log_handler`` configuration item.
- support Odoo config files with multiple comma separate databases names
in db_name config entry.

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- pass click ctx to environment_manager

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- refactor ``click_odoo.env_options`` to allow propagating ``env``
to subcommands through the click context. Fixes 16.
- do not log click Exit exception, which may be raised by subcommands as
a result of --help.

Upgrading:
- click-odoo now requires click>=7

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- add ``with_addons_path`` option to ``click_odoo.env_options``
to control the presence of the ``--addons-path`` option. Defaults to False.
Enabled for the ``click-odoo`` CLI.

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- add ``environment_manager`` to ``click_odoo.env_options``, providing
a hook on ``odoo.api.Environment`` creation.
- add ``--addons-path`` option to the CLI.
- add ``database_must_exist`` option to ``click_odoo.env_options``
so scripts can behave how they please in case the database is absent.

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- silence deprecation warning
- adapt tests for Odoo 12