Add support for opening counsel-git-grep in other window

[flooose]

Adds functionality described in related issue

[flooose]

Heyhey, my copyright assignment just got in. What do next steps look like? Do you need a copy of the document?

[basil-conto]

Heyhey, my copyright assignment just got in.

Excellent! :tada:

What do next steps look like?

I'll merge this as soon as I get a chance over the coming days :).

Do you need a copy of the document?

No need, I was already CCed in the email from the copyright clerk.