This change adds a inhibition cache. New alerts are checked against all
inhibition rules' source matchers. At notification time, we only have to
check the target matchers against the notified alerts. If there are
alerts in the source cache, we only have to verify the equal labels
against these.
No longer update components based on a new configuration. Generally,
destroying and recreating has no performance impact and is less
error-prone.
This also removes the Reloadable interface and simplifies the entire
startup contraption.
