Added the auto-fill feature to ProductControl.
1. When the main Form loads, it calls MakeMap() in its constructor.
2. MakeMap checks for "Products.txt" in its working directory (during development, this is bin/Debug).
3. MakeMap accordingly creates a Dictionary called mapStore which houses a Product Number -> Pair(Product Name, Product Rate) mapping.
4. ProductControl objects are made to call SetMapping so that their own Dict object refers to the one in the main Form.
5. A TextChanged event handler in ProductControl deals with checking for entries in Product No field, and automatically appending Product Name and Rate to their corresponding fields.
6. Tested to be working fine, have used similar idea in modified DataProSoft.