Change wording of verification email etc.

[Ben Jones]

I would like to be able to change the wording of

etc.

[Michał Powaga]

@yogiben You can do it like that:

PrettyEmail.defaults.verifyEmail =
  heading: 'Need to activate your account'
  buttonText: 'Activate'
  ...

[Ben Jones]

Great. Please update readme when making appropriate commits.