Large item-tree matrix crashes browser

[Letme]

Recently I discovered that if you render an item-tree with large amount of items, the build takes a lot longer, but the most problematic thing is that when user tries to view the page the whole page has to be loaded in browser and it crashes the browser. Too much item and then too much javascript to hide it. This issue makes high memory usage on build, and drains memory for users when rendering.

My proposed solution would be that item-tree and item-matrix (as well as attribute-matrix) paginate the results (above user defineable level). Extension should generate more HTML pages for the huge item-tree and then use javascript (ajax, jquery) to progressively load them on demand. Also, it should provide build time warning (with sane default, but ability to change in conf.py, since it is dependant on the build infrastructure) when number of items exceeds it to alert users about this problem (and usage of :paginate: number_of_items_per_page attribute to item-matrixes).