Move require rotp library to the file where it is used

[gkopylov]

It is ok when I check it in development environment, but when I run some tests there are many errors uninitialized constant Devise::Models::TwoFactorAuthenticatable::InstanceMethodsOnActivation::ROTP. I think it is because require 'rotp' is not in appropriate place.

[gkopylov]

Btw there are some another problems(perhaps because I am using it with mongoid). For example, I need to require 'two_factor_authentication/models/two_factor_authenticatable.rb' directly in my User class, so without it I getting error uninitialized constant Devise::Models::TwoFactorAuthenticatable. And yet another problem is that after all that done(that I mentioned above) there are still some errors like undefined method is_fully_authenticated?' for #UsersController:0x000000037358b8. It seems that method is_fully_authenticated?` is not added as a helper to ApplicationController. Any thoughts about it? Or it better to create another issue for that? Again, all is ok, when I just use it, but errors appear when I run my tests with rspec.