Initial implementation of products
Added relations between products and brands
Added API for products. Products are completely ready.
Contribution support for people (without API)
Added contribution support for organisations and product detail page (without API)
Added contributions API (without contributions info in ProductAPI as it's not clear what is needed
Fixes after code review
 - two tables renamed;
 - several comments fixed;
 - improved code style;
 - error on product removal caused by assigned contributors fixed;
 - several UI improvements.
Remove redundant evolutions