Unify and simplify Check / AsyncCheck, ACheckConfig / AsyncCheckConfig.

Hinting at further changes to unify permission access and caching. Later
permission caching can also be done for moving checks, though checking
for the current thread may be exchanged in favor of config flags.
Generic configuration will allow to set individual timeouts for checks,
check groups and default. There could also be change policies like
"world change only", possibly listening to permission updates, if
feasible.

CheckData / AsyncCheckData are not as simple to unify, if we want to
keep the footprint as low as possible there. There could even be more
implementations to match different policies.
More spaces.