Move remaining feature interfaces into Microsoft.AspNetCore.Http.Features package and namespace

- related to #561
- move required interfaces and classes down from `Microsoft.AspNetCore.Http.Abstractions`
- move everything in the `Microsoft.AspNetCore.Http.Features` into their own directory

nit: remove transient dependencies listed in `Microsoft.AspNetCore.Http.Abstractions`'s `project.json`

Author: dougbu

src/Microsoft.AspNetCore.Http.Abstractions/project.json

@@ -29,13 +29,10 @@
     },
     "netstandard1.3": {
       "dependencies": {
-        "System.ComponentModel": "4.0.1-*",
         "System.Globalization.Extensions": "4.0.1-*",
         "System.Linq.Expressions": "4.0.11-*",
-        "System.Net.WebSockets": "4.0.0-*",
         "System.Reflection.TypeExtensions": "4.1.0-*",
-        "System.Runtime.InteropServices": "4.1.0-*",
-        "System.Security.Cryptography.X509Certificates": "4.0.0-*"
+        "System.Runtime.InteropServices": "4.1.0-*"
       },
       "imports": [
         "dotnet5.4"

src/Microsoft.AspNetCore.Http.Abstractions/CookieOptions.cs renamed to src/Microsoft.AspNetCore.Http.Features/CookieOptions.cs

@@ -4,7 +4,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 
-namespace Microsoft.AspNetCore.Http.Features.Internal
+namespace Microsoft.AspNetCore.Http.Features
 {
     public interface IFormFeature
     {