Fix all custom stoploss samples

docs/strategy-advanced.md

@@ -24,8 +24,12 @@ To simulate a regular trailing stoploss of 4% (trailing 4% behind the maximum re
 
 ``` python
 # additional imports required
-from freqtrade.persistence import Trade
 from datetime import datetime
+from freqtrade.persistence import Trade
+
+class AwesomeStrategy(IStrategy):
+
+    # ... populate_* methods
 
     use_custom_stoploss = True
 
@@ -70,6 +74,13 @@ Of course, many more things are possible, and all examples can be combined at wi
 Use the initial stoploss for the first 60 minutes, after this change to 10% trailing stoploss, and after 2 hours (120 minutes) we use a 5% trailing stoploss.
 
 ``` python
+from datetime import datetime, timedelta
+from freqtrade.persistence import Trade
+
+class AwesomeStrategy(IStrategy):
+
+    # ... populate_* methods
+
     use_custom_stoploss = True
 
     def custom_stoploss(self, pair: str, trade: Trade, current_time: datetime, current_rate: float,
@@ -89,6 +100,13 @@ Use a different stoploss depending on the pair.
 In this example, we'll trail the highest price with 10% trailing stoploss for `ETH/BTC` and `XRP/BTC`, with 5% trailing stoploss for `LTC/BTC` and with 15% for all other pairs.
 
 ``` python
+from datetime import datetime
+from freqtrade.persistence import Trade
+
+class AwesomeStrategy(IStrategy):
+
+    # ... populate_* methods
+
     use_custom_stoploss = True
 
     def custom_stoploss(self, pair: str, trade: Trade, current_time: datetime, current_rate: float,
@@ -111,6 +129,13 @@ The below example sets absolute profit levels based on the current profit.
 * Once profit is > 20% - stoploss will be set to 7%.
 
 ``` python
+from datetime import datetime
+from freqtrade.persistence import Trade
+
+class AwesomeStrategy(IStrategy):
+
+    # ... populate_* methods
+
     use_custom_stoploss = True
 
     def custom_stoploss(self, pair: str, trade: Trade, current_time: datetime, current_rate: float,