Fix logoset caching.

[LindirQuenya]

This resolves #280.

Previously: the preference-changed event for logoSet (and hence the requests for the new logos, so that they can be displayed below the dropdown) was emitted without waiting for the UPDATE_PREFERENCES signal to be sent to the backend. This was caused by a combination of throttling and using send instead of request. It resulted in a mixture of the previous and correct logo sets - some logo requests were processed by the backend pre-change, some post-change. The "new" images, once requested, were cached by the frontend until the next logoSet change.

Now: for logoSet only, we await the completion of the backend request before emitting the preference-changed event.

[coveralls]

Pull Request Test Coverage Report for Build 2401468646

• 14 of 22 (63.64%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.6%) to 56.604%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/shared/preferences/util.ts	3	11	27.27%
<!--	Total:	14	22	63.64%	-->

Totals
Change from base Build 2397456263:	1.6%
Covered Lines:	399
Relevant Lines:	627

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💛 - Coveralls