ui: update for different reg fee assets

[chappjc]

With registration fees accepted in different assets, as reported by the regFees field, the UI needs to be updated to allow selection of the fee asset according to what the server supports.

The workflow will also change a bit since DCR isn't required any more and the /register workflow should jump from init to add a dex instead of forcing a DCR wallet setup first.

Something that looks like this perhaps:

Originally posted by @chappjc in #1202 (comment)

[chappjc]

@vctt94 is starting this. If anyone has started or has ideas, please comment now.

My general idea for how this dialog should work:

• click on row of table, it will somehow show as selected, maybe a subtle highlight or boundary or different background
• the New Wallet button I prototyped looks like crap though, so this should look nicer
• when a row is clicked ideally some text will be shown above the Register button: "When you submit, a fee of "

So I guess some JS to handle the click action, which does the style change for the table and updates / creates the text I just mentioned