Add blacklist check to BinModel#latest
Add binLoadCallback
update load and latest to use binLoadCallback
Return the result of the original method from metrics wrapper

We do this because our higher order function requires a return value,
previously, all the methods took a callback rather than returning
a value so its understandable that this wasn't in place
Merge pull request #1558 from jsbin/feature/blacklist-load

Feature/blacklist load