Remove a dependency cycle involving StreamPlayer, StreamPlayerEvent and StreamPlayerEventLauncher.

[HelgeStenstrom]

Plus fixed a spelling error.

The cycle is removed by

• Make use of StreamPlayerInterface instead of StreamPlayer in StreamPlayerEvent
• Stop sending the source as a part of the event. The source was one link in the cycle.

Description

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What kind of change does this PR introduce? (check at least one)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
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Does this PR introduce a breaking change? (check one)

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• [ *] No

Has This Been Tested?

• [ *] Yes, a little
• No

Checklist:

• My code follows the style guidelines of this project
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