Added helm to the popup ignore list

[azy2]

Helm manages it's own windows and doesn't interface with popup very well.

[hlissner]

I'm afraid I can't accept this into Doom. I consider this as a personal customization and would rather leave this to private modules than make this the default, for a couple reasons:

1. I've tried to model the helm and ivy modules to act visually similar to CtrlP (vim), Goto-Anywhere (sublime text/atom), and command-T (textmate), as a reasonable default, and leave it to users to undo or change in their customizations. I agree that the whole-frame approach doesn't suit widescreens well, but I'd like to implement child frame support to address this instead.
2. The completion/helm module's defaults work fine with feature/popup. If this is not the case, that is a bug.
3. It is easier to put (set! :popup "^\\*helm" :ignore) in a private config than it is for another user to either remove that rule from display-buffer-alist or define a new rule to shadow the old one simply to reinstate the fallback behavior of +all.

[azy2]

That seems reasonable to me. I didn't think it would do anything to the default setup and I figured it would make customizing helm less confusing. It certainly took me awhile to figure out why my helm settings weren't applying. Perhaps there's a fix in popup that's less drastic than :ignore that maintains the original behavior.