Add delete button for Articles

[vs2961]

At the moment, drafts cannot be deleted on the cms. Add a button that allows admins to delete them.

[AndySok]

can admins delete drafts using rails c?

[vs2961]

Yes, and as an afterthought, there should also be a button that turns an article back into a draft.

[AndySok]

For devs: if you can make this button work, you won't have to do anything else for the rest of the year

[mjiang97]

A delete button could be made accessible on each individual draft but to more efficiently delete drafts, we could implement a "select" button so that multiple drafts can be deleted at once. We could then place deleted drafts into another group so that we can recover multiple drafts, again using the "select" button (a "recover" button should also be added to individual drafts).