is
Equals
Ensures ordering of `PossibleTemplates` does not affect tests.
checkOrigin
check
More consistent with `Issue.ctor`'s "template".
Includes moving the origin check back to templates, constructing nested template classes in each check, and making parameterized template usage.
IssueTemplate
Issue
As a result we can also make check an interface, and need to provide the check itself when constructing an issue.
Check
BeatmapCheck
We're probably not going to need GeneralChecks or BeatmapsetChecks. The verify tab is only available to a single difficulty at a time, and we already have access to the rest of the set through `IBeatmap`.