Remove `launchsettings.json` entry from `.gitignore`. Closes #760 (#761)

Do not ignore launchsettings.json. Closes #760

As discussed in:
https://github.com/github/gitignore/pull/2705
https://github.com/github/VisualStudio/issues/1405

src/Microsoft.DotNet.Web.Spa.ProjectTemplates/content/Angular-CSharp/.gitignore

-/Properties/launchSettings.json
-
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 

src/Microsoft.DotNet.Web.Spa.ProjectTemplates/content/React-CSharp/.gitignore

-/Properties/launchSettings.json
-
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 

src/Microsoft.DotNet.Web.Spa.ProjectTemplates/content/ReactRedux-CSharp/.gitignore

-/Properties/launchSettings.json
-
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.