feature: displaying a warning before opening a block explorer link

[chitowncrispy]

Description

I added a new UIAlertController to display an alert to the user when they tap on a block explorer link. I also made a slight refactor to remove the delegate that is passed into EventDetailViewModel.swift. I replaced it with a more reactive approach to more fully embrace that style of programming within the app.

Motivation and Context

This is to address issue #125.

How Has This Been Tested?

On the iOS simulator, I went to the history page, tapped on a transaction and then tapped on both transaction hashes as well as addresses. I verified that the cancel button dismissed the alert in both cases. I also verified that the continue button took us to the correct block explorer page in both instances.

I also went to the channel page and tapped on the funding transactions. I verified that the cancel button dismissed the alert. I also verified that the continue button took us to the correct block explorer page.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #326 into master will decrease coverage by 0.14%.
The diff coverage is 17.5%.

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
- Coverage   10.71%   10.56%   -0.15%     
==========================================
  Files         247      247              
  Lines        9803     9827      +24     
==========================================
- Hits         1050     1038      -12     
- Misses       8753     8789      +36

Impacted Files	Coverage Δ
Library/Extensions/UserDefaults.swift	0% <ø> (ø)	⬆️
Library/Generated/strings.swift	6.97% <ø> (ø)	⬆️
Library/Coordinators/WalletCoordinator.swift	0% <0%> (ø)	⬆️
Library/Extensions/UIAlertController.swift	0% <0%> (ø)	⬆️
...nes/History/Detail/EventDetailViewController.swift	0% <0%> (ø)	⬆️
Library/Tests/EventDetailViewModelTests.swift	97.36% <100%> (+2.49%)	⬆️
...y/Scenes/History/Detail/EventDetailViewModel.swift	36.29% <62.5%> (-1.93%)	⬇️
...htning/Services/Misc/BlockChainHeightUpdater.swift	60.41% <0%> (-20.84%)	⬇️

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[ottosuess]

Greenwallet has an option to turn that alert off. that's pretty nice for users who don't care about that notification.

We can just store that in the UserDefaults. (https://github.com/LN-Zap/zap-iOS/blob/master/Library/Extensions/UserDefaults.swift).

[chitowncrispy]