Add stop-loss/take-profit market orders

[holzeis]

The flow

stop loss market: price < X -> trigger market order take profit market: price > X -> trigger market order

Coordinator-based notification

1. user sets a price
2. if price is reached, user gets a push notification / or websocket notification
3. if user comes online, the user triggers a order and executes it

App-based notification

1. user sets a price
2. if user is online, the app checks if the price has been reached and triggers the order.