Create Meetup OmniAuth Rails Example App

Adds to the RailsApps OmniAuth authentication menu a choice for Meetup. Any preferred OmniAuth provider replaces Twitter in additional places now.

Creates a new preference, 'collect_user_email.' If false, this strips all email-related user registration code from any generated OmniAuth Rails Example App.

Creates a new Rails Example App, 'rails3-mongoid-omniauth-meetup,' which:

* Utilizes OmniAuth Meetup authentication; and
* Doesn't collect users' email addresses.

Alters the specs from 'rails3-mongoid-omniauth' for the new Rails Example App.

Generates without error message:

* The RailsApps template;
* The new Rails Example App;
* Existing Rails Example App, 'rails3-mongoid-omniauth.'

The new app was tested using ERB. With Haml or Slim (translations of the view), no attempt has been made (yet) to remove (upon request) the user registration email-related functionality.

With that caveat, all gem, 'rails_apps_composer' tests pass. All tests pass in the following generated Rails Example Apps:

* The new Rails Example App;
* Existing Rails Example App, 'rails3-mongoid-omniauth.'

The two generated Rails Example Apps (above) seem to work fine, and browser login succeeds.