User:
	id
	username (may be NULL, because of possible OpenID/Google/Facebook/etc.  login)
	openid
	google
	facebook
	github (is it possible?)
	stack exchange (is it possible?)
	yahoo
	password (may be NULL, see username)
	e-mail
	skills

Skill:
	ID
	approved?
	short name
	description

Company:
	ID
	name
	slug (must be specified during company registration, user must accept or change it; will be available at the URL /company/{slug})
	description
	co-worker list (list of Users with permissions)
		ID
		Can register Products on behalf of company?
	contact e-mail address

Product:
	ID
	name (short description, 100-150 characters)
	description
	subprojects (list of Teams)
	Product Owner (a specific User)
	owning company (a Company, or NULL)
	Idea Pool (list of Ideas)
	Product Backlog (list of UserStories)
	sprints (list of Sprints)
	discussion (a specific Discussion)

Team:
	ID
	Scrum Master (a specific User)
	members (a list of Users)
	name
	skill requirements (list of Skills)

Idea:
	ID
	short description
	long description
	team estimated difficulties (list of Team/Difficulty pairs)
	team estimated development times (list of Team/Time pairs)
	author (a specific User)
	discussion board (a specific Discussion)

# UserStories are Ideas, extended with Tasks. UserStories are always created
# from Ideas, and as such, all the fields of Ideas are copied to the UserStory
UserStory:
	ID
	short description
	long description
	team estimated difficulties (list of Team/Difficulty pairs)
	team estimated development times (list of Team/Time pairs)
	author (a specific User)
	discussion board (a specific Discussion)
	tasks (a list of Tasks)

Task:
	ID
	short description
	long description
	discussion (a specific Discussion)

Sprint:
	ID
	start date
	length
	sprint goal
	sprint backlog (a list of UserStories)
	discussion (a specific Discussion)

Discussion:
	ID
	messages (a list of Messages)

Message:
	ID
	Author (a specific User)
	timestamp with time zone
	subject (may be NULL)
	body