Inefficiency with BListItem + BListView design

[smallstepforman]

BListView retrieves item metrics from BListItem (in order to handle selection, scrolling etc). This is essentially a pointer list transversal, which isn't a performant memory access operation during scrolling / selection. A better design would be to store the item metrics in a vector inside BListView, this works better with cache locality since it no longer needs to jump around memory searching for a visible item. Insertion/deletion will be slower, but that is not the frequent operation. T