Track version checking

[hsoi]

Expand the default analytics functions provided by HEAnalytics to provide mechanisms for tracking in-app version checking (e.g. using https://github.com/nicklockwood/iVersion)

Something like:

func newVersionDisplayAlert(newVersion: String?)
func newVersionDownload(newVersion: String?)
func newVersionReminder(newVersion: String?)
func newVersionIgnore(newVersion: String?)