Update HMI images

In order to showcase technologies used by Apertis and have more demonstrative official images, this commit installs the following Flatpak applications along with the multimedia demo pack:

• Rhythmbox (music player)
• Totem (video player)

In addition to showcasing the use of Flatpak apps on Apertis, those also allow one to test the system's audio and video playback abilities.

Finally, the flatdeb demo application is also installed on target images in order to demonstrate Flatpak apps built using a custom, flatdeb-generated runtime.

Finally, the target images are renamed to HMI so their name is more explicit.