Add board ordering/reordering capability to the issue list

Description

Right now, gitlab board supports drag & drop ordering of issues in each board. However, it is not reflected in the issue list at all. It is great if:

1. The ordering can be seen in the issue list, e.g. having the possibility to order issues by their 'board priority order'!
2. Enable drag & drop ordering in issue list, just like the way it is possible in the issue board

Proposal

I don't know how the current 'ordering' in boards is implemented. However, if it is a 'local ordering' with respect to the board, it can be instead a 'global' ordering. Or, maybe its better to remain as a local ordering with respect to the boards, and boards themselves represent an ordering with respect to each other.

Links / references

It can be considered an updated request to add 'priority' support to the issue list. Which currently exists with 'priority labels' (which are really not easy to work with), and apparently 'weights' which are 1. only available in EE 2. doesn't seem to be easy to work with too!

Documentation blurb

1. Why should someone use it; what's the underlying problem: It connects the board and the issue list more closely, which is a good thing. :P
2. Add total ordering to issues without using explicit numbers and/or labels
3. How does someone use this: using drag & drop with a mouse, or maybe similar functionality using a keyboard

Thanks!