Implement adding a stock to the stocks page

[Christiane (Tina) Heiligers]

The API to create a stock accepts a stock symbol.
Implement adding a new stock with the following requirements:

1. The end user should be able to provide the stock symbol
2. The stock is added if it is not a duplicate
3. If the stock already exists, then the user is notified thereof (preferably before issuing the api request)
4. The new stock is automatically added to the list of stocks in the table
5. There is a success notification to inform the end user that their request was successful.