Remove PersistentTimer's dependency on DiscordInterface

[kevinlul]

Description

Part of #161. I think even the intermediate code can be removed from TournamentManager; instead of the link seams, the two key functions can be dependencies, so that the delegate can directly call Eris instead of another level of indirection through DiscordInterface, which might be worthwhile depending on how long TournamentManager sticks around without being ripped up.

Checklist

• I am following the contributing guidelines.

[coveralls]

Pull Request Test Coverage Report for Build 561807932

• 11 of 16 (68.75%) changed or added relevant lines in 2 files are covered.
• 11 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 75.869%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/TournamentManager.ts	3	4	75.0%
src/timer.ts	8	12	66.67%

Files with Coverage Reduction	New Missed Lines	%
src/TournamentManager.ts	11	65.16%

Totals
Change from base Build 550179999:	-0.3%
Covered Lines:	892
Relevant Lines:	1113

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💛 - Coveralls

[AlphaKretin]

Sorry that I left this in the lurch, it completely passed my notice.