"No Magic Strings" for Event names

[mixmix]

If we're using event emitters in keyring:

• make one events.js file, put all the events in there
• import named events
• document the events in that file?
• feel bad when that file gets too big

[mixmix]

e.g.

export const ACCOUNT_UPDATE = 'account-update'
/* this is emitted when.... */
export const ACCOUNT_CREATE = 'account-create'

[frankiebee]

closing in favor of #439