Start and Restart Stream Keeper.

[rashtrakoff]

It's possible that a dHEDGE pool can disable a deposit asset i.e., the asset will no longer be allowed to be deposited into the dHEDGE pool. However, the streams of all users will still exist. In case the asset is disabled for a long time, the streams need to be stopped as they are not generating any yield for the users. When the asset is re-enabled, the streams should be re-started. However, this process should not take place frequently. This is because we will be unable to cover the gas costs associated with such frequent stream modifications. We should only close streams if the fees that we will get is more than the costs to manage every users' streams. Maybe we can only service those markets which actually generate enough profits to make stream management possible ?