[SQUASH] Address PR comments.

* Split Parameter into IntParameter/FloatParameter/CategoricalParameter.
* Rename IHyperStrategy to HyperStrategyMixin and use it as mixin.
* --hyperopt parameter is now optional if strategy uses HyperStrategyMixin.
* Use OperationalException() instead of asserts.

freqtrade/optimize/hyperopt.py

@@ -23,6 +23,7 @@ from pandas import DataFrame
 from freqtrade.constants import DATETIME_PRINT_FORMAT, LAST_BT_RESULT_FN
 from freqtrade.data.converter import trim_dataframe
 from freqtrade.data.history import get_timerange
+from freqtrade.exceptions import OperationalException
 from freqtrade.misc import file_dump_json, plural
 from freqtrade.optimize.backtesting import Backtesting
 # Import IHyperOpt and IHyperOptLoss to allow unpickling classes from these modules
@@ -68,7 +69,11 @@ class Hyperopt:
 
         self.backtesting = Backtesting(self.config)
 
-        if self.config['hyperopt'] == 'HyperOptAuto':
+        if not self.config.get('hyperopt'):
+            if not getattr(self.backtesting.strategy, 'HYPER_STRATEGY', False):
+                raise OperationalException('Strategy is not auto-hyperoptable. Specify --hyperopt '
+                                           'parameter or add HyperStrategyMixin mixin to your '
+                                           'strategy class.')
             self.custom_hyperopt = HyperOptAuto(self.config)
         else:
             self.custom_hyperopt = HyperOptResolver.load_hyperopt(self.config)