Linux: implement 'focus' property of Window to set initial focus

For #424
set transport_security_state for HTTPS connections

So we can launch https sites in debug mode
Win: implement 'focus' property of Window to set initial focus

Fix #424
Mac: implement 'focus' property of Window to set initial focus

For #424
[README] Add guide for redistributing the binary with license notice

Fix #1081
add process.versions['chromium']

Fix #1052
add window.closeDevTools()
[Mac] Fix #1043: don't constrian window frame