API updates and fixes

- 'filename' parameter is now required when uploading a product file
and order item option file
- Uploading product file now allows setting file description
- 'lastUpdateTime' in product details is renamed to 'updated'
- 'usdTotal' is not needed when updating or creating an order
- explanations for the 'productPrice' field in the orders endpoints
- removed 'shippingMethodId' field from the orders endpoints
- added endpoint to remove all files attached to an order item option
- removed 'activeOrdersCount' field from customers search response
- added internal gallery image IDs in the Get product method response