[IMPR] Allow all Site.categorymembers() parameters for Category.subcategories()

• enable all parameters of Site.categorymembers() with Category.subcategories() method
• drop cache because a lot of parameters are used now
• call Category.members() to implement Category.subcategories to prevent code duplication
• update tests

Change-Id: Iad5570767cbe497e107d8b8f989bc50a7ef16560