Make block edit links easier to edit/turn off individually

Currently, the $edit_links_array is a simple un-keyed array of rendered links. While its easy to add links to this array and re-render the $edit_links var, its difficult to remove links or to modify the links because you have to search through the entire array using strpos (or something similar) to find the link you want.

The easy solution to this is to add unique keys to each array item.

For example, sub-themes could then just edit $edit_links_array['block-config'] directly.