queue-level exclusive jobs

[Skn0tt]

At the moment, it's possible to have both exclusive and non-exclusive jobs on the same Queue. In practice, all usecases have either fully-exclusive queues (queues where all jobs are exclusive) or fully non-exclusive queues (queues where no jobs are exclusive). This PR makes some changes to move the concept of being exclusive up a layer: It treats any Queue that ends on exclusive as being exclusive, thus saving one Redis call.

Notably, this PR is missing:

• [ ] a migration path
• [ ] any decision on wether this change is actually worth it

[coveralls]

Pull Request Test Coverage Report for Build 1055645602

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 87.315%

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Files with Coverage Reduction	New Missed Lines	%
src/shared/tracer.ts	2	86.67%
<!--	Total:	2		-->

Totals
Change from base Build 1052936781:	-0.03%
Covered Lines:	435
Relevant Lines:	462

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💛 - Coveralls