Zocalo

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* Drop support for Python 3.5
* Update language constructs for Python 3.6+

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* Add support for Python 3.9

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* Remove stomp.py requirement - this is pulled in via workflows only

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* Set live flag in service environment if service started with '--live'

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* Start moving dlstbx scripts to zocalo package:
* zocalo.go
* zocalo.wrap
* Entry point 'dlstbx.wrappers' has been renamed 'zocalo.wrappers'
* Dropped Python 3.4 support

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* Compatibility fixes for graypy >= 1.0