Complete take_over

[Changaco]

Reticketed from #1948. We've already taken steps towards completing take_over, this issue is to keep track of what's still missing:

• fix the merge UI
• merge ui should give you the option to make the other account primary (was merge ui should give you the option to make the other account primary #675)
• merge statement (was merging accounts should merge statements #834)
• merge exchange routes (was Lost card association after merging accounts #941)
• archived accounts should be removed from teams (was archived accounts should be removed from teams #1920) (fixed in Fix giving and receiving amounts #2718)
• merge email addresses

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[chadwhitacre]

+1 for deciding which account to make primary:

https://twitter.com/thattommyhall/status/512983370889187328
https://twitter.com/whit537/status/512984306583863296

[chadwhitacre]

fix the merge UI

What does this entail? From #2752 (comment) I suggest showing emails on the merge ui.