QML components revamping part 2

This MR is a revamping of the Qt desktop GUI based on what's been proposed in terms of design on the Zeplin: https://app.zeplin.io/project/5e271dc7628e287e59163571

It's also based on the following document where I try to have a "canonical reference" for colors to iterate upon: https://code.videolan.org/bunjee/vlc/-/wikis/colors

It also changes the play button behavior with a "scale on click" behavior à la Spotify.