This is an improvement over #107, to make the application entirely responsive (up t a certain point, but which should not be encountered even on mobile).
Most changes are either very small or only permit a seamless compatibility with low-width displays; the three only "big" changes happening are:
- under 800 pixels wide, the bottom playing bar elements see their relative width change a bit, to allow give enough space for the song name and player control, without having a big blank space on the right
- under 950 pixels wide, the queue tracks list has less margin, to allow to fit way more of the song names
- under 750 pixels wide, the current song's cover and name is hidden from the left of the queue tracks list: this permits to continue fitting the content, and this information is redundant anyway as it is show on the bottom playing bar already
