Decouple Databus from SessionManager

[srenfo]

This moves the Databus object out of the SessionManager. This allows future tests to instantiate SessionManagers without bothering with the databus.

[coveralls]

Pull Request Test Coverage Report for Build 1186

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 93 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.4%) to 72.654%

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Files with Coverage Reduction	New Missed Lines	%
conpot/protocols/http/web_server.py	3	85.71%
conpot/protocols/enip/enip_server.py	7	63.87%
conpot/protocols/ftp/ftp_handler.py	9	82.93%
conpot/protocols/ftp/ftp_base_handler.py	13	80.12%
conpot/protocols/http/command_responder.py	61	54.73%
<!--	Total:	93		-->

Totals
Change from base Build 1181:	-0.4%
Covered Lines:	5505
Relevant Lines:	7577

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💛 - Coveralls

[srenfo]

Let me know if this change is too small or too non-consequential. I can bunch up such changes instead.