Setting up CodeCov again

[StanleyGoldman]

• Using nuget to get opencov and codecov binaries
• Providing a powershell script to produce code coverage
• Using said script in AppVeyor
• Excluding some flaky tests from code coverage

[StanleyGoldman]

Test comment

[codecov]

Codecov Report

Merging #1902 into master will decrease coverage by 2.54%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1902      +/-   ##
=========================================
- Coverage   40.94%   38.4%   -2.55%     
=========================================
  Files         487     487              
  Lines       18868   18669     -199     
  Branches        0    2450    +2450     
=========================================
- Hits         7726    7169     -557     
+ Misses      11142   10954     -188     
- Partials        0     546     +546

Impacted Files	Coverage Δ
...ViewModels/GitHubPane/PullRequestCheckViewModel.cs	1.09% <0%> (-81.32%)	⬇️
.../GitHub.Exports/Helpers/NotificationAwareObject.cs	0% <0%> (-50%)	⬇️
...ws/ViewModels/PullRequestReviewCommentViewModel.cs	72.41% <0%> (-25.87%)	⬇️
...InlineReviews/Models/PullRequestSessionLiveFile.cs	80% <0%> (-20%)	⬇️
src/GitHub.App/Services/Translation.cs	42.42% <0%> (-19.7%)	⬇️
...Hub.InlineReviews/Models/PullRequestSessionFile.cs	75% <0%> (-18.75%)	⬇️
src/GitHub.App/Services/OAuthCallbackListener.cs	82.35% <0%> (-17.65%)	⬇️
src/GitHub.App/Services/RepositoryCloneService.cs	75.86% <0%> (-13.8%)	⬇️
src/GitHub.Exports/Models/LocalRepositoryModel.cs	51.31% <0%> (-13.62%)	⬇️
src/GitHub.UI/Helpers/LoadingResourceDictionary.cs	54.83% <0%> (-12.91%)	⬇️
... and 133 more

[jcansdale]

Looks good to me. 👍