PageBrowser: allow changing nb of chapter levels shown (#8772)
PageBrowser: allow changing nb of chapter levels shown (#8772)

Instead of using the depth configured in Book map, start
with max depth, and allow decreasing (and reseting when
at 0) with long-press on the (i) top left icon.
poire-z/koreader,Frenzie/koreader,koreader/koreader,Frenzie/koreader,NiLuJe/koreader,NiLuJe/koreader,poire-z/koreader,koreader/koreader