ControllerScriptEngineBase: install console extension

[Swiftb0y]

This allows new scripts to use console.* functions which for example
enables easier debugging using Qt's debugging and logging tools.
See https://doc.qt.io/qt-5/qtquick-debugging.html#console-api for more information
on the console extension api.

I already suggested this while reviewing another PR: #4171 (comment)

[coveralls]

Pull Request Test Coverage Report for Build 1097682922

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 26.027%

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Totals
Change from base Build 1097150390:	0.01%
Covered Lines:	20019
Relevant Lines:	76915

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💛 - Coveralls

[Be-ing]

How about doing this in ControllerScriptEngineBase?

[Swiftb0y]

It was already one in the ModuleScriptEngine subclass as well. So I guess I can pull up both into the base class.

[Holzhaus]

Can we replace print() in common-controller-scripts.js with console.log and remove the log() method of the controller engine?

[Be-ing]

Good idea to change common-controller-scripts.js. I'm not sure we should remove the old log function though. There is only one script in Mixxx that uses it for the Hercules DJ Console 4 Mx, but there might be old mappings on the forum using it. It doesn't hurt to keep it. Maybe we could change the implementation in ControllerScriptEngineLegacy to forward it to console.log though.