Mongoid support

[exocode]

it implements the ability to use mongoid

[tessi]

@mediatainment thanks for your pull request! I'd love to see mongoid being supported. I am currently quite busy (nobody warned me about this thing called "real life" when i was young ;)).

I will review and comment on your PR as my time allows.

[tessi]

@exocode I am back and currently collect changes for version 2.0.0

If you are still interested, could you please apply some changes to your PR?

• Rebase this PR on the new master

• Each Database module now has a little setup code:

  # lib/capistrano/uberspace/mongoid.rb
  
  module Capistrano
    module Uberspace
      module Mongoid
      end
  
      self.database_module = Mongoid
    end
  end

  This helps for auto-detecting the default database and is a potential place for common helper functions. Would be great if you'd follow that new convention.

• Could you also please add a dump task to mongoid.rake (take inspiration from the other databases)?
  Then we'd have a database dump feature for all databases.

• The icing on the cake would be if you could test the whole thing (when ready) on a fresh uberspace to make sure the setup code works correctly.