Basic HTTP/2 support. Disabled by default. Warning added to the enabl…

[honfika]

…e flag:

• only enabled when both client and server supports it (no protocol changing in proxy)
• GetRequest/ResponseBody(AsString) methods are not supported
• cannot modify the request/response (e.g header modifications in BeforeRequest/Response events are ignored)

Doneness:

• Build is okay - I made sure that this change is building successfully.
• No Bugs - I made sure that this change is working properly as expected. It doesn't have any bugs that you are aware of. At least in the existing code when the HTTP/2 flag is disabled
• Branching - If this is not a hotfix, I am making this request against the master branch

[honfika]

Hi @justcoding121

There is a new example project in this commit, called: Titanium.Web.Proxy.Examples.Wpf.NetCore.csproj
This is the .net core version of the existing WPF application. Since .net framework does not supprot ALPN, I'm using this project for testing. This project is not added to any solution.
It needss .net core 3.0 preview sdk and maybe VS 2019 (I don't have 2017 installed, so could not test it).

[honfika]

BTW, I'm usign this site for testing: https://http2.akamai.com/demo
In this PR version the WPF app shows the http2 tunnels and the http sessios inside the tunnel, but ony the headers ars shown.

I'm working on it to support the reading of the body, too.