Refactor cache context to support correct parallel execution

We need a new service, IParallelCacheContext, which allows
tracking the current cache context across threads and tasks
running in the thread pool.

--HG--
branch : 1.x

src/Orchard.Core.Tests/Common/Providers/CommonPartProviderTests.cs

@@ -55,6 +55,7 @@ namespace Orchard.Core.Tests.Common.Providers {
             builder.RegisterType<DefaultShapeFactory>().As<IShapeFactory>();
             builder.RegisterType<StubExtensionManager>().As<IExtensionManager>();
             builder.RegisterType<StubCacheManager>().As<ICacheManager>();
+            builder.RegisterType<StubParallelCacheContext>().As<IParallelCacheContext>();
             builder.RegisterInstance(new Mock<IThemeManager>().Object);
             builder.RegisterInstance(new Mock<IOrchardServices>().Object);
             builder.RegisterInstance(new Mock<RequestContext>().Object);

src/Orchard.Core.Tests/Settings/Metadata/ContentDefinitionManagerTests.cs

@@ -50,6 +50,7 @@ namespace Orchard.Core.Tests.Settings.Metadata {
                 .As(typeof(IMapper<SettingsDictionary, XElement>));
             builder.RegisterType<Signals>().As<ISignals>();
             builder.RegisterType<StubCacheManager>().As<ICacheManager>();
+            builder.RegisterType<StubParallelCacheContext>().As<IParallelCacheContext>();
 
             _container = builder.Build();