This commit is the culmination of multimedia/elisa!205

Notable Changes:
- Added mobile folder with components needed for mobile (and are separator from desktop components)
- Changed tst_NavigationActionBar test so that it does not check for artist button when it is invisible (loaders are used now so the button wouldn't be detected)
- Added loaders in ContentView.qml to switch between the mobile and desktop sidebars
- Changed ContextView.qml to use FormLayout, and also add mobile navigation buttons
- Collapsed the two list delegates (detailed and non detailed) together, along with edits for mobile usage
- Lowered the size of text in list delegates
- Extracted out the settings form to be shared between mobile and desktop
- Edited the grid delegate to be mobile friendly
- Removed clip from both listviews and gridviews for performance
- Extracted out the volume slider and duration slider to be shared for mobile and desktop
- Add mobile and desktop component switching for MediaPlayListView.qml
- Port the metadata view into Kirigami FormLayout so that it can be shared between mobile and desktop
- Rework NavigationActionBar buttons to all be components loaded in by loaders, so that we can have different layouts for mobile and desktop
- Extract shared properties for playlist delegates between mobile and desktop into BasePlayListDelegate.qml
- Extract shared properties between media players on mobile and desktop into BasePlayerControl.qml