Make Django account for stock limits on trade page
Make Django account for stock limits on trade page

Now it checks that you haven't given yourself or someone else too many
stocks when you are trading. There are a few more things to do.

1. Make the received trade page do similar checks.

2. Make the StockSuggestion model check if adding a stock would give
someone too many stocks, and if so, just add it to the floor.

Make progress on #17.

ddsnowboard/FantasyStocks,ddsnowboard/FantasyStocks,ddsnowboard/FantasyStocks