Hastexo-xblock

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* [Bug fix] Make Paramiko SSH connections more robust against socket
timeouts (and retry the connection if it runs into one).

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* [DEPRECATION] As of this release, the previous implementation that
relied on the Guacamole Tomcat servlet is deprecated. A `stable-4.1`
branch exists that might still receive bugfixes for some time, but
do not count on this being supported any longer than the lifetime of
the Open edX Koa release. The [Ansible
playbooks](https://github.com/hastexo/edx-configuration/tree/hastexo/juniper/hastexo_xblock)
that tie into `edx-configuration` have been updated to “do the right
thing” based on the hastexo XBlock version being deployed: for
version 5 and up, they deploy Daphne and pyguacamole; for earlier
versions, they continue to deploy Tomcat and the Guacamole servlet.

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* [Bug fix] Add a default `port` value for `rdp` connections.

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* Merge recent changes from 4.1 into 5.0 RC branch.

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* [Bug fix] Fix `read_only` mode `key` and `mouse` event filtering
logic.

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* [Enhancement] Implement the `read_only` mode in the websocket
consumer by not passing any `key` or `mouse` events to `guacamole`
when set to `True`.
* [Bug fix] Include `stack_protocol` attribute when initializing the
javascript code so that the terminal height value will be calculated
correctly.
* [Bug fix] Refactor asyncio task creation logic to also work with
python3.5.
* [Bug fix] Add missing dependencies for `hastexo_guacamole_client`.