Improve the design of the call-out to select a default search provider

[rmisio]

The design IMHO just looks "broken". It looks odd that the triangle area points between the first and the second item. The first thought is always that it should be pointing to an actual item and we've even had a bug logged about that. I understand that the idea is for it not to point to an item, but rather to the group, since you need to select an item. But... there's just got to be a better way to reflect that.

[jjeffryes]

Something that came up in discussion:

It might be better to start with no search providers, and give the user a modal that lists the defaults, with a short description of each, and allow them to add them. They could make one of them the default while doing that, or if they just add one it's automatically the default.

This would let us include a message saying we can't vouch for the content on 3rd party providers, and the user would have to make a conscious choice to add providers that may have content we don't vouch for, vs. 3rd party providers being added by default.