Adds login analytics

[bummytime]

This PR does the following:

• Now captures all of the login analytics emitted by WordPressAuthenticator via the WordPressAuthenticatorDelegate
• Tracks the logout event in SettingsViewController
• Explicitly adds the WordPressShared pod to our Podfile (it is needed in WooAnalyticsStat.swift to convert a WPAnalyticsStat to a WooAnalyticsStat)

Fixes: #33

Testing

First, blow away 💥 the ./Pods folder in your local repo and run pod install. Then launch XCode and make sure the app builds and the unit tests are ✅.

Next run through the various Authentication flows while verifying that you are seeing logs like:

🔵 Tracked login_email_form_viewed

in the console. You should not see any logs like:

⚠️ Could not convert WPAnalyticsStat with value: 99

Finally after a few minutes, open the tracks live view and verify you see the auth/logout events.

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@jleandroperez & @mindgraffiti would either of you mind taking a peek at this?

[mindgraffiti]

all unit tests passing ✅
events reporting in console ✅
events reporting in tracks ✅

Working great, thank you @bummytime.

One question: an event reported as:
WooCommerce[50670:2387890] 🔵 Tracked signed_in, properties: [AnyHashable("dotcom_user"): "true", AnyHashable("multifactor"): "false"]. I use 2FA to log in. Does "multifactor" mean something else?

[mindgraffiti]

Shipping on behalf of Bummy, who is AFK today :)

[bummytime]

Thanks for reviewing and merging this @mindgraffiti!

One question: an event reported as:
WooCommerce[50670:2387890] 🔵 Tracked signed_in, properties: [AnyHashable("dotcom_user"): "true", AnyHashable("multifactor"): "false"]. I use 2FA to log in. Does "multifactor" mean something else?

TBH, I am just forwarding along the props dictionary that the Authenticator pod sends to our delegate. Perhaps this is a bug there? Maybe @jleandroperez has some insight?