qt: introduce album sections (Gsoc 2025)
This intends to supersede !7485.
Many thanks to @GlaucousGlaucus for his efforts. I have taken the model change as is, and started from scratch for the rest (QML/Quick side) with the ideas in mind that we discussed in the said merge request, and with some parts copied such as building the caption label.
Also many thanks to @chub for the discussions, especially for the current section indicator idea.
Screenshots:
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Recording: