Add omniauth to let huginn consume oauth endpoints

Created a service model which stores external account information.
Created a service controller which kicks off the oauth process and lets
the user manage their external accounts.
Oauthable concern connects a agent to a service and adds a drop down to the
agents edit page.
Added a migration which converts the existing twitter agents to use the
new service model.
Update new agent form to include the service dropdown

When creating a new agent the service dropdown needs to be updated after
switing the agent type. Rendering the whole form and cherry picking just
the needed services dropdown seemed the easierst solution.
Added documentation about how to set up OAuth applications
User#available_services make sure to escape the parameters, added
missing link to the wiki
Fixed services migration, disabled agents after deletion of a service
Skip validations in the oauth migration

Also enforced the presence of needed attributes of the services table on
the database level
OAuthable concern now uses class instance variables
Merge remote-tracking branch 'huginn/master' into omniauth
Fixed the specs
Merge remote-tracking branch 'huginn/master' into omniauth

Conflicts:
	app/models/agents/basecamp_agent.rb
	app/models/user.rb
	db/schema.rb
	spec/fixtures/agents.yml
Merge branch 'master' into omniauth

Conflicts:
	Gemfile.lock
	app/controllers/agents_controller.rb
Import scenarios with agents which need a service
Unified the layout of devise forms
Renamed 37signals environmental variable to not start with numbers
Use 'net-ftp-list' gem to parse ftp directory listing.

It also parses non-unix ftp servers, which have a different list format.
Merge pull request #426 from PetroFeed/ftpsite_whitespace_fix

Use 'net-ftp-list' gem to parse ftp directory listing.
Use boolify().
Fix #423 "cloud service" link broken
Fixed seeds and fictures for rain notifier

The seed rain notifier wasn't using liquid templates so the
conditions and location showed up as literal strings.
Merge pull request #428 from andrewcurioso/master

Fixed seeds and fixtures for rain notifier