There is a distinction between packages which are already
installed on the local machine and packages which are
available on the remote server. Even with this difference
it is important that they are handled the same and can be
reused in the same GUI elements.
In order to reduce code duplication I created a parent object
PackageList which contains the base logic and interface for
the QML and let both RemotePackageList and LocalPackageList
inherit from this.
UX specified that the gear icon (Settings.svg) should be
separate from the tabs of material and plugins. This also
ment that the current tab item couldn't set the pageTitle
anymore. This is now defined in the Package component and
set when the loader has loaded the external QML file.
Contributes to CURA-8558
