Reacted to aspnet/Razor#215 changes.
Add out-of-order HTML attributes to MVC tag helper sample
- these are rendered in the same, non-alphabetic order
- demonstrates aspnet/Razor#225 does not affect HTML attributes
Fix #1618, Add asp- prefix to custom attributes of MVC tag helpers
- update XML docs to reflect new HTML / custom attribute separation
- update `Exception` messages to use new attribute names
- update MVC tag helper sample to use new custom attribute names
- add missing `<input/>` tag helper `throw`s test

nits:
- reword a few comments and messages for clarity and consistency
- use `<exception/>` sections to describe what's thrown
- add "Reviewers" comments about current throws
 - note `<a/>` and `<form/>` are slightly inconsistent with others: `throw`
   if unable to override specified `href` or `action` attributes; rest
   `throw` only if custom attributes are inconsistent e.g. `<input/>` with
   `asp-format` but no `asp-for`
- create test tag helpers after all property values are available
Add functional test of MVC tag helper sample
- ensure future changes don't break this sample
CR feedback from [ModelBinderAttribute]
Adding Support for TryUpdateModel using include expressions and predicate.
Fix for #1671 - Adding [FromHeader] attribute
Updating to release NuGet.config
Updating to dev NuGet.config
random cleanup
Fix for #1681 - Model state errors are wrong with attributes like [FromHeader]

The issue here is that a model state error is added with the model name
'doubled'. This is on a fairly obscure code path and the code dates back
to the original WSR git checkin of webapi. There are no wsr tests that
verify this behavior.

The cause here is that our 'greedy' model binders (like
FromHeaderModelBinder) return 'true' whether or not they successfully
found a model, because they don't want other model binders to run.

This also has an effect on the validation system. That means that
validators will run and attempt to validate the model (which may be null).
That's that rare case where we get to this code path.
Merge branch 'release' into dev
Adding servers and wwwroot folder to test websites

Adding dependencies and commands for iis, web listener and khestrel to each
site.

Each website comes with a readme.md to 'anchor' the otherwise empty
folder. We have another work item tracking adding content to these.

Once VS sees a project with a wwwroot, it wants to assign a port for iis,
so I let it.
Update names of WebSite projects for consistency

Project/Assembly names are all like 'FeatureWebSite' root namespaces
updated accordingly. This makes processing all of the functional tests and
deploying the web sites much simpler.
Update WebAPI shim functional tests to use a header for payload

The issue is that responses to HEAD cannot have a body. When running these
tests on a real server, they break because the server throws when you try
to write to the body.
Update precompilation to use the library manager instead of relative
paths.

This website is written to assume that $pwd is always in the functional
tests directory when it's launched. This works fine for the functional
tests, but causes issues in many other contexts, including VS.
update comment about precompilation (cr feedback)
Changes to address IFileSystem.Watch method addition

Absorbs the new IFileSystem interface. This change is to just address the breaking change introduced in IFileSystem.
Razor has to do the necessary changes to subscribe to the Watch event for expiring the modified files.
Remove use of `Assert.DoesNotThrow()`
- no longer in xunit :smiley:
Removing transitive references from aspnetcore50 to unblock build