[suggestion] create wiki page to document ordering

I suggest to create a wiki page to start documenting the ordering mechanism. The whole ordering is currently not very well documented and there are many classes (e.g. GridViewOrdering, LeafGridViewOrdering, LocalOrdering, LeafLocalOrdering, DirectLeafLocalOrdering,...) where the usage is not directly obvious (at least not to me). I think it would be a good idea to have a document stating the general idea and structure of the ordering and a list of the involved classes along with their function (which might be used to update/create the doxygen comments in the code). This would greatly help when trying to understand and debugging the code. This page could also contain a description of the blocking-mechanism which would be very helpful in scenarios with a more complicated blocking structure.

Currently I am not allowed to create or modify wiki-pages and was thus not able to start an example/basic page.