FXIOS-615 ⁃ Add caching and prefetch of breach alerts data

[vphong]

Currently, the breach alerts manager loads data every time the logins list is loaded - specifically in viewWillAppear(). This creates more network requests than necessary. An optimization that could be made is to call the network request earlier, save the result from that request in a cache, load the LoginsListViewController with breach data from the cache, and update the cache on a longer time interval to reduce network requests.

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