Create a reusable dialog component

[aaroncox]

Work with Max to design and implement a custom dialog component that we can use/extend throughout Unicove.

This came up and could be implemented for two purposes right now:

1. When switching accounts during a multisig configuration, we should notify the person about how their new account works. Right now it just switches your account and brings you to the new accounts homepage, with no explanation of what exactly the multisig wallet does.
2. On the msig page, you can approve/cancel/execute the msig proposal. None of these actions result in a Transaction Summary at the end that shows you the status/error of the transaction, and there's no way to find the transaction easily. When performing actions on these pages which originate from a single button click, it should popup with a dialog that shows the transaction summary.

The dialog should work on both desktop and mobile.

I'm sure there's plenty of other places we'll find this useful in as well!