Fix for U4-4493

Makes it possible to go back if you don't want to customize.
Fix for U4-4913
Updated modals.less

Added background color to umb-dialog footer
Updated sortdiaglog frame

Updated the dialog frame to use dynamic height.
U4-4931 - lock contention & potential application lockdown

Conflicts:
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs
	src/umbraco.cms/Actions/Action.cs
U4-4931 - fixing & refactoring

Conflicts:
	src/Umbraco.Core/Cache/DictionaryCacheProviderBase.cs
	src/Umbraco.Core/Cache/HttpRuntimeCacheProvider.cs
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs
U4-4931 - fixing & refactoring
U4-4931 - fixing & refactoring

Conflicts:
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs
U4-4931 - fixing & refactoring

Conflicts:
	src/Umbraco.Core/Cache/DictionaryCacheProviderBase.cs
	src/Umbraco.Core/Cache/DictionaryCacheWrapper.cs
	src/Umbraco.Core/Cache/DictionaryItemWrapper.cs
	src/Umbraco.Core/Cache/HttpRequestCacheProvider.cs
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs
U4-4931 - do not cache exceptions

Conflicts:
	src/Umbraco.Core/Cache/DictionaryCacheProviderBase.cs
	src/Umbraco.Core/Cache/HttpRequestCacheProvider.cs
U4-4931 - fixing & refactoring

Conflicts:
	src/Umbraco.Core/Cache/DictionaryCacheProviderBase.cs
	src/Umbraco.Core/Cache/HttpRequestCacheProvider.cs
	src/Umbraco.Core/CacheHelper.cs
	src/Umbraco.Core/Umbraco.Core.csproj
	src/Umbraco.Tests/Cache/HttpRequestCacheProviderTests.cs
U4-4931 - fixing & refactoring

Conflicts:
	src/Umbraco.Core/Cache/HttpRequestCacheProvider.cs
U4-4931 - also for ObjectCacheRuntime provider

Conflicts:
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs
Merge branch '7.1.5' into 7.1-4931
Merge branch '7.1.5' into 7.1-4931
Merge branch '7.1.5_U4-5316' of https://github.com/bjarnef/Umbraco-CMS into bjarnef-7.1.5_U4-5316

Conflicts:
	src/Umbraco.Web.UI.Client/src/views/common/dialogs/mediapicker.html
	src/Umbraco.Web.UI.Client/src/views/propertyeditors/colorpicker/multicolorpicker.controller.js
fixed bug where root element is documents and not documentSet
copy past error
added some ToArray() to ensure execution
Set up database level paging for retrieving child content for list view