Py-trees

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* [infra] missed the py_trees exec dependency, fixed.

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* [docs] faq added
* [tutorials] 9 - bagging
* [infra] various dependency fixes for tests and autodoc
* [tests] fix broken subscrirber test

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* [tutorials] 8 - dynamic loading, insertion and execution
* [tutorials] 7 - docking, undocking, cancelling and recovery

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* [infra] add missing actionlib dependencies

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* [js] performance improvements, `120 <https://github.com/splintered-reality/py_trees_js/pull/120>`_
* [js] highlighted links, `115 <https://github.com/splintered-reality/py_trees_js/pull/115>`_
* [js] orthogonal link connections, for better visualisation
* [qt] capture screenshots, `114 <https://github.com/splintered-reality/py_trees_js/pull/114>`_

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* [html] disable scrollbars, `110 <https://github.com/splintered-reality/py_trees_js/pull/110>`_
* [js] robustness against identical timestamps, `109 <https://github.com/splintered-reality/py_trees_js/pull/109>`_
* [js] improved window resize handling, `111 <https://github.com/splintered-reality/py_trees_js/pull/111>`_
* new public api ``py_trees.canvas.on_window_resize`` and ``py_trees.timeline.on_window_resize``