Add TagHelper functional test.

- Added an end-to-end test that verifies all content behaviors, interactions and functionalities of tag helpers.
- Added some common user scenarios to verify that the system works how we expect.

#1116
React to UsePerRequestServices
Update new test to use UsePerRequestServices
Add TagHelperSample.Web
Address tag helper sample code review comments and reflect offline discussion
- lots of new comments in Create.cshtml