GlobalDrawer: Clean up (part 2)

Flatten out nested sub-components

The sheer amount of indentation was getting hard to read on a FullHD screen.

Port to required properties, relax types to T.Action

The plan is to get rid of modelData usages.

Drop visibility from colorSet binding

What's the point of changing colorSet of an invisible item anyway?

Port away from modelData

Replaces modelData and hasOwnProperty spaghetti with typed checks and self-descriptively named shorthand properties.

Fixes inconsistencies between visibility bindings on expanded and non-expanded representations of ActionDelegate: non-expanded variant lacked "children.length" check, and the expanded variant forgot to check whether an action is visible at all.

Cleaned up some qualified properties access; moved ToolTip out of superfluous data list.

Remove polyfills for Qt 5.9

Remove unused property wideMode