Notification: Date Parsing Failsafe

We're now making sure that *timestampAsDate* property (*Notification* class) always returns a valid date, in order to prevent any grouping bug.

Plus: the error is logged in console + a typo in UIView+Helpers.swift has been patched

Fixes #2350 

/cc @sendhil 

Thanks in advance!
What's a Failasfe?