Replace references to HttpPlatformHandler with AspNetCoreModule

[Tratcher]

Announcement: aspnet/IISIntegration#105

Here are the required template changes for reference: aspnet/Templates#450

Search:
https://github.com/aspnet/Docs/search?p=3&q=HttpPlatformHandler+&utf8=%E2%9C%93

• Lots of Web.Config samples
• Severs: https://github.com/aspnet/Docs/blob/29c3d17ddefb669ce2a1b3253fb6e30255bfa706/aspnet/fundamentals/servers.rst#L149
• Nano: https://github.com/aspnet/Docs/blob/0c3d55a0753f0c30e91ac698b4c52154bd39764b/aspnet/tutorials/nano-server.rst#L56
• Document how to debug when hosted on IIS using AspNetCoreModule #577
• IIS hosting scenarios coverage with the aspNetCore element #786

@danroth27

[shirhatti]

And this entire article as well https://github.com/aspnet/Docs/blob/master/aspnet/hosting/http-platformhandler.rst

[danroth27]

Opened #1348 to track the Servers doc updates

[rachelappel]

Nano doc modified for ASP.NET Core module (https://github.com/aspnet/Docs/blob/0c3d55a0753f0c30e91ac698b4c52154bd39764b/aspnet/tutorials/nano-server.rst#L56)