SPF: Refactor navigation so that all external functions are executed inside try/catch to gracefully handle errors.  Callbacks may return false to cancel but errors thrown will be logged and ignored.
SPF: Refactor navigation so that all external functions are executed inside
try/catch to gracefully handle errors.  Callbacks may return false to cancel
but errors thrown will be logged and ignored.


[git-p4: change = 55525662]

scrapp-uk/spfjs,nicksay/spfjs,youtube/spfjs,nicksay/spfjs,theanh/spfjs,tchiotludo/spfjs,nicksay/spfjs,youtube/spfjs,theanh/spfjs,scrapp-uk/spfjs,DavidCPhillips/spfjs,scrapp-uk/spfjs,youtube/spfjs,DavidCPhillips/spfjs,tchiotludo/spfjs,nicksay/spfjs,tchiotludo/spfjs,theanh/spfjs,nicksay/spfjs,scrapp-uk/spfjs,theanh/spfjs,DavidCPhillips/spfjs,tchiotludo/spfjs,youtube/spfjs,scrapp-uk/spfjs,DavidCPhillips/spfjs,theanh/spfjs,youtube/spfjs,tchiotludo/spfjs