Full working CEF on GNU/Linux

Hi fellows and friends and Epic Team

I thought I like to share my progress I on an old PR about CEF on GNU/Linux and made it work with all needed keys. Copy, Paste and Cut and the WebBrowserWidget works too.
See here using SlateViewer YouTube

Ok, now the WebBrowserWidget works too. See here: https://www.youtube.com/watch?v=lAbXmXnBmro

Ok, finished. Made a PR for this. Here you can test if you like

https://github.com/EpicGames/UnrealEngine/pull/977

Read the description about the issues please. If you want to try this PR do not forget to compile UnrealCEFSubprocess.