Convert webvfx filter to QML

It took a few maneuvers for this one.

QML doesn't have native support for tooltips (except for Button, go figure). For other filters, some tooltips got lost during the conversion process. But for this one, it seems the tooltips are important. So I created a crude ToolTip component and tried to match the native look of tooltips the best that I could.

Also, it might be a good time to discuss the organization of files in src/qmltypes. Maybe QmlFile and QmlHtmlEditor should be moved or renamed? I'm open to comments.
To be more consistent with Qt QML style, I recommend to rename this as mousePos() and possibly as a Q_PROPERTY. "Mouse" is more obvious and natural. I know QCursor::pos() is static, but as soon as you put "Utilities {}" into QML, it makes an object.