Remove arguments from QQuickWebEngineSettings signals

The convention in the rest of the QtQuick API is to not pass the new
value of a changed signal as an argument since the signal handler can
easily access the property itself.

Change-Id: I0dbf70379f631135c5ad973b46a9f3936d4be115
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Fix the inspector

Add the missing implementation of
DevToolsHttpHandlerDelegate::EnumerateTargets allowing WebEngineViews
to appear in the remote debugging's discovery page.

This code was mostly taken from
content/shell/browser/shell_devtools_delegate.cc

Change-Id: I2759d7c424adf4d7acb779a64e0083032691d9ba
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Use the Chrome inspector discovery page

The content_shell discovery page is missing some CSS
and causes the favicon to repeat as the background.

Copy the one from Chrome and change it slightly to
remove the page thumbnail.

Change-Id: I6aaa12d5c9d5abdbc4dd5c297a69445aa478045e
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>