add tooltips

[oliviamriley]

i think it would be good to add little pop-up tooltips next to fields to give a little info. stuff like the from field is what we use to sign in to your chosen provider (unless it's custom, in which case we provide a username).

this would also be a good way to inform users about mail.com and easy smtp setup. maybe a tooltip on the dropdown? all of this info should be in the documentation, too.

[oliviamriley]

bootstrap documentation here shows how to do this easily