Fixed what Keys managedCefBrowserAdapter send

Problem: Not all input-keys was sent to handled in Javascript, especially keycombinations like Strg + X, Strg + V and so on wasn't handled. Now, with the fix, this is no longer a problem. Also the keys, special handled in the original version, are no longer needed and so i removed them.
Startpage "about:blank" removed

Problem: The Back-Button doesn't work on the right way, because the with about-blank he's activated (like you can press the button) but doesn't load anything, because about:blank isn't a real site. So the running-statusbar always running, but no progress is visible. Also there was the possibility, that the real Url never loaded. Don't know how these works together, but with an empty startpage, this problem is gone.
Removed special key-combination strg+shift, only used for own project
Merge branch 'master' of https://github.com/g3st3/CefSharp
Revert fix for #522
Example of user land fix for #522