Add "Preferred Wallets" array to config

[aaroncox]

It should be possible to present 1-3 wallets as the "preferred wallets" in the configuration of the plugin.

These plugins would be displayed as the primary options, when a large list of wallets is provided to the renderer. A "more wallets" option would be available to then show the full list.

This would be useful to set Anchor, CloudWallet, Scatter as the preferred wallets, but also include support for cleos and any other power user wallets that the developer may want to hide by default.

The preferred wallets should probably be a non-list design that presents these wallets front and center. We'll need a new design for this most likely.

[aaroncox]

Note how WalletConnect handles this, displaying 3 select wallets at the bottom with a "View All" option.