Adds fancy alert warning if site's WC is lower than v3.5

[bummytime]

This PR adds the following a fancy alert warning if the users current site is below WC v3.5 (below REST API v3). The version check and subsequent alert (if needed) is fired every time the app enters the foreground.

Breakdown of items here:

• Fancy alert dialog implementation (FancyAlertViewController+Upgrade.swift)
• App Delegate updates → helper func (displayWooUpgradeAlertIfNeeded) and FancyAlert appearance
• UIViewControllerTransitioningDelegate conformance in MainTabBarController
• Implementing the namespaces call in our arch stack (SiteAPI model, SiteAPIRemote, SiteAPIMapper, new SettingStore action)
• Unit tests

Note: The retrieveSiteAPI action bypasses the Storage framework to keep things simple.

Note2: This PR is an analogue to the following WCAndroid PRs:

• V3 API: Update WooCommerce version warning card copy woocommerce-android#524
• Dashboard: Add WooCommerce 3.5 update prompt woocommerce-android#521
• Woo: Add action for fetching the max supported WooCommerce version wordpress-mobile/WordPress-FluxC-Android#990

Fixes: #398

Testing

Make sure code is square and unit tests are ✅ .

Scenario 1: Log into a WC site v3.5 or newer

1. Log into the site
2. Verify no warning alert is displayed after the site picker is dismissed
3. Background the app
4. Bring the app into the foreground and verify the alert does not display

Scenario 2: Log into a WC site v3.5 or older

1. Log into the site
2. Verify the alert warning alert is displayed after the site picker is dismissed
3. Background the app
4. Bring the app into the foreground and verify the alert displays again
5. On the warning dialog, tap the "Update Instructions" link and verify the web page loads in a new modal.

@jleandroperez and @mindgraffiti I know this PR looks gigantic, but it's really just the testing JSON....honest! 😃

/cc @kyleaparker @aforcier @astralbodies

[wpmobilebot]

	1 Warning
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

SwiftLint found issues

Warnings

File	Line	Reason
FancyAlertViewController+Upgrade.swift	57	Files should have a single trailing newline.

Generated by 🚫 Danger

[jleandroperez]

One cosmetic comment, other than that, works like a charm!!!

[jleandroperez]

(Already discussed over Slack!!) Maybe move this guy over to RequirementsChecker or so?

(Feel seriously free to disregard, this is a cosmetic suggestion!!)

[bummytime]

Thanks @jleandroperez ... I ended up adding RequirementsChecker :-)