Add FundingOpportunity

[PGijsbers]

Inherits from News and defines:

funder	Agent	0-n		The entity funding the opportunity.
type	String	0-n
opening_date	datetime	0-1		The start date of the application for the Fundind Opportunity.
closing_date	datetime	0-1		The end date of the application for the Fundind Opportunity.
minimum_contribution	decimal	0-1		The lowest amount of funding that can be requested or granted for the opportunity.
maximum_contribution	decimal	0-1		The highest amount of funding that can be requested or granted for the opportunity.
announcement_page	URL	0-1		The location where sites the original announcement.
submission_platform	URL	0-1		The location where sites the platform for the submission.