Add new analytic event: Universal webview fail event

[g-opzt]

We have an event vama_login_fail that was originally designed to capture when logins failed at the point of the webview reporting an error. (i.e. the webview itself crashing or running into an error. If the website within has an error this doesn't count)

We use webviews in several other parts of the app, so ideally we'd have universal tracking of this in a new event:

• [ ] vama_webview_fail captures any time a webview crashes/reports an error similar to the specific event above. It would also capture a parameter webview that stores the link for which URL the webview launched so we can differentiate between where in the app it occurred and, if possible, error that stores the returned error message.

[alexandec]

We have a useExternalLink hook that's called whenever the user taps on an external link. Currently that hook sends the vama_link_click and vama_link_confirm events. We could add a new vama_link_error event there. That said, I don't know for sure if we'd actually get any errors, or what type they might be.