Create user account authorization features according to specific roles

[ScriptyChris]

Shop may offer it's features for different user roles:

• client who can:
  • view products (should not require to have an account)
  • buy products [Implemented basic integration with PayU API #27] (maybe user should be able to buy a product without being logged in? kind of ad-hoc shopping)
  • add review for bought products [Implemented add review feature #40]
  • check purchase info (like delivery status, invoice retrieval, refunding)
  • manage favorites/observed products [Extended client account management and improved handling User session #46]
• seller/retailer who can:
  • view products
  • add new products
  • edit already added products [Implemented modifying products API #18, Added UI for modifying product feature #38]
  • see added products statistics (sales, views)
  • request shop administrator to add new category
  • moderate products reviews
• administrator who can:
  • do some maintenance activities
  • TBD...
• all of them can:
  • change their account details (like: password [Extended client account management and improved handling User session #46], email, avatar)
  • logout from active sessions