The refresh enumerator is intended to refresh an enumerator stack
after the stack has been exhausted. The existing implementation
refreshed the enumerato stack on EVERY MoveNext invocation leading
to data being dropped.
This commit addresses two existing issues:
1. The datasource is refreshed half as often as it should
2. Data points are emitted on every data source refresh
This places all security subscriptions within a universes
Subscriptions generated via calls to AddSecurity are place in a UserDefinedUniverse
UserDefinedUniverse will serve up a predetermined list of symbols on a requested interval
LiveTradingDataFeed - reworked custom enumerators to use RefreshEnumerator as wrapper for rate limitting
Michael Handschuh