Expose additional context

[RobbeSneyders]

This PR contains 2 main changes:

• Expose additional context. We now expose the scope, operation, connexion context, and receive channel as context aware globals. This makes them available to the decorators independent of the framework in between. The user will also be able to use these.
  I also implemented a TestContext class which can be used to populate the context during testing. It's minimal, but can be extended towards the future.
• Rename the decorators to be framework specific. This is part of a bigger change for which I'll submit a follow up PR. I was working on this first when it became clear that the context would need to be extended, which is why this is already included.

[coveralls]

Pull Request Test Coverage Report for Build 3876472127

• 137 of 154 (88.96%) changed or added relevant lines in 11 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 90.629%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
connexion/apps/async_app.py	1	2	50.0%
connexion/decorators/response.py	6	7	85.71%
connexion/testing.py	40	43	93.02%
connexion/lifecycle.py	9	14	64.29%
connexion/decorators/main.py	24	31	77.42%

Files with Coverage Reduction	New Missed Lines	%
connexion/decorators/main.py	1	72.9%
connexion/lifecycle.py	5	71.79%

Totals
Change from base Build 3876399595:	-0.1%
Covered Lines:	3143
Relevant Lines:	3468

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💛 - Coveralls