wallpapers/picture: Use org.kde.plasma.wallpapers.image
applets: Import appchooser
shell: Rename AppletError errorMessage to reason

This is how the Plasma API calls it.
shell: Remove AppletError id
shell: Have AppletError align icon and text to the top and wrap

Improve the presentation and also use text color from theme.
appchooser: Start working on the layout
appchooser: Import Kicker plugin

We cannot import the Kicker plugin because it's private so we
must copy and rename it here.
appchooser: Rename plugin to org.hawaii.appchooser.private

Plasma's PackageUrlInterceptor only recognize org.kde.plasma.private.$name
and expects the applet to be called org.kde.plasma.$name so it happens
that we cannot import our private plugin.

PackageUrlInterceptor should support applets with a name that doesn't
start with org.kde.plasma.  Until it does we rename our plugin to
something that won't be detected as a private plugin.

This means that other applets may use our private plugin though.
appchooser: Fix typo in metadata.desktop
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.