Add global usings (#668)

* Use global usings

* Fix namespace declarations for test projects

src/Spectre.Console/Enrichment/CI/AppVeyorEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class AppVeyorEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/BambooEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class BambooEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/BitbucketEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class BitbucketEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/BitriseEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class BitriseEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/ContinuaEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class ContinuaEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/GitHubEnricher.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class GitHubEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/GitLabEnricher.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class GitLabEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/GoCDEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class GoCDEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/JenkinsEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class JenkinsEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/MyGetEnricher.cs

@@ -1,6 +1,3 @@
-using System;
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class MyGetEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/TeamCityEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class TeamCityEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/TfsEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class TfsEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/CI/TravisEnricher.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console.Enrichment;
 
 internal sealed class TravisEnricher : IProfileEnricher

src/Spectre.Console/Enrichment/ProfileEnricher.cs

@@ -1,7 +1,3 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-
 namespace Spectre.Console.Enrichment;
 
 internal static class ProfileEnricher

src/Spectre.Console/Enrichment/ProfileEnrichment.cs

@@ -1,5 +1,3 @@
-using System.Collections.Generic;
-
 namespace Spectre.Console;
 
 /// <summary>