Continued with project:

Continued with project:
- Used "category" instead of "id" for category selection box
- Added method addProduct()
- Added method isProductTitleUsed()
- Added new exception ProductTitleAlreadyUsedException
- Changed parameter type of "parent" to Integer as it can be done (better type-hint)
- Rewrote addCategory() a bit for this
- Added database columns "category", "price" and "title" for products
- Renamed method isCategoryUsed() to isCategoryTitleUsed()
- Deleted do_products.jsp
Signed-off-by:Roland Häder <roland@mxchange.org>