EngineControl: Use mixxx::audio::FramePos

[Holzhaus]

Some work towards using frame positions in the engine.

[coveralls]

Pull Request Test Coverage Report for Build 1117774890

• 94 of 153 (61.44%) changed or added relevant lines in 11 files are covered.
• 998 unchanged lines in 17 files lost coverage.
• Overall coverage increased (+0.0003%) to 25.998%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/engine/controls/enginecontrol.cpp	9	11	81.82%
src/engine/positionscratchcontroller.cpp	0	3	0.0%
src/engine/controls/bpmcontrol.cpp	6	10	60.0%
src/engine/controls/loopingcontrol.cpp	30	36	83.33%
src/engine/controls/vinylcontrolcontrol.cpp	0	7	0.0%
src/engine/controls/cuecontrol.cpp	30	67	44.78%

Files with Coverage Reduction	New Missed Lines	%
src/engine/controls/cuecontrol.cpp	1	68.94%
src/engine/controls/loopingcontrol.cpp	1	82.97%
src/engine/controls/vinylcontrolcontrol.cpp	1	50.46%
src/engine/sync/internalclock.h	1	80.0%
src/track/beatgrid.h	2	60.0%
src/util/db/dbconnection.cpp	5	69.78%
src/engine/sync/internalclock.cpp	16	80.51%
src/library/dao/directorydao.cpp	17	75.61%
src/engine/sync/synccontrol.cpp	38	82.46%
src/engine/sync/enginesync.cpp	44	85.11%

Totals
Change from base Build 1104640684:	0.0003%
Covered Lines:	20015
Relevant Lines:	76988

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💛 - Coveralls

[Holzhaus]

Let me know if the diff is too big, I can cherry pick individual commits into separate branches if you want.

[uklotzde]

LGTM, waiting for CI

[uklotzde]

CI failure is unrelated.