auto refresh service

[nreese]

There are currently several places in Kibana that manage their own auto refresh logic. This includes courier, timelion, and several locations in x-pack.

Courier's SearchPoll has logic to throttle the refresh interval timeout to the speed that courier can execute when the interval is too fast.

All auto refresh logic should to be combined into a single service. This service should use the SearchPoll logic so that the refresh timer can be throttled to the speed for the slowest request when the interval is too fast.

This issue is created in response to #20863. 20863 introduced a temporary fix for auto refreshing visualization panels in dashboard. Part of the converstation for the temporary fix involved creating a proper auto refresh service. The event autoRefreshFetch should be replaced by the auto refresh service