[UX] Many accounts makes menu overflow

[TheLonelyGhost]

See an example in the demo copy of the application. If there are too many accounts to fit on the screen in the top menu dropdown, there is no way to get to the ones at the bottom of the list.

One easy solution might be to add a route in Backbone for /accounts that will list all accounts available for the currently logged-in user account. We might also change the link "Accounts" at the top menu bar to go to that page and have a hover/focus event open the dropdown, mirroring the current functionality.

Making a fully-fledged page enumerating all of the accounts might also make it a bit more mobile-friendly, I'd imagine.