Add support for binary frames

[jhugard]

Current API appears to only support Text frames, and will convert the received string from UTF-8 to a UTF-16 string. Not so good for working with binary protocols, including Google Protocol Buffers.

[ngoel17]

Is anybody planning to support this?

[kolbma]

https://github.com/kolbma/Websockets.PCL/commits/master

1. kolbma@f334f4d
2. kolbma@c7b7132
3. kolbma@aba609d

Could someone test the iOS changes? Or provide the environment for testing?

Do we need to support WP8?
It isn't available in VS 2017.

[kolbma]

@NVentimiglia Could we upgrade the dependencies to newer versions?
The cert checks on UWP can only be disabled on the Anniversary Version.
Also the newer androidasync brings many bugfixes.