Fix for issue 72

https://github.com/mikeedwards83/Glass.Mapper/issues/72
removing the obsolete attribute  for SitecoreAttributeConfigurationLoader
remove net 4 assemblies
Removed .NET 4 assemblies from MVC4 nuget package
Amend sorting logic

Need to amend sorting logic as it will default to 0 and therefore break if you want to override it.
fix for error messaging
small fix to resolving of type configuration when creating items
Merge branch 'master' of github.com:mikeedwards83/Glass.Mapper
Merge branch 'develop' of https://github.com/mikeedwards83/Glass.Mapper into develop

Conflicts:
	Source/Glass.Mapper.Sc/CodeFirst/GlassDataProvider.cs
Merge remote-tracking branch 'mike/master' into develop

Conflicts:
	Powershell/BuildScripts/Glass.Mapper.Sc.Mvc-4.symbols.nuspec
	Powershell/BuildScripts/Glass.Mapper.Sc.Mvc-5.symbols.nuspec
	Source/Glass.Mapper/Context.cs