appchooser: Add icon name role

We don't want to use QIcon from QML, we already have our own Icon
item that applies a shader to change symbolic icon colors and is
capable of showing an Image with non-colored icons.
appchooser: Expose AppsModel to QML
appchooser: Add entryPath property to AppsModel

Setting entryPath one can filter the categories shown by the model.
An empty entryPath (default) shows all the categories.
appchooser: First layout attempt

Use AppsModel and do a first draft of the layout.
appchooser: Add accessibility to item list delegate
appchooser: Add description role to the model

Even if the name may take that into account already we may need
the description to do a different visual style than the
name label.
appchooser: Add description label to delegates
appchooser: Add search entry

Doesn't do much yet.
lookandfeel: Don't clip users view

This make users visible even if they are totally or partially outside the
component area.