Introduces fast declaration style for factory

Created by: stefanoborini

Makes it faster to define the factory by specifying just the class, factoring out the boilerplate of the reimplementation of the method.

This is backward compatible with the current plugins

force_bdss/data_sources/base_data_source_factory.py

-import abc
-from traits.api import ABCHasStrictTraits, provides, String, Instance
+import logging
+from traits.api import ABCHasStrictTraits, provides, String, Instance, Type
 from envisage.plugin import Plugin
 
-from .i_data_source_factory import IDataSourceFactory
+from force_bdss.data_sources.base_data_source import BaseDataSource
+from force_bdss.data_sources.base_data_source_model import BaseDataSourceModel
+from force_bdss.data_sources.i_data_source_factory import IDataSourceFactory
+
+log = logging.getLogger(__name__)
 
 
 @provides(IDataSourceFactory)
@@ -19,14 +23,22 @@ class BaseDataSourceFactory(ABCHasStrictTraits):
     #: A human readable name of the factory. Spaces allowed
     name = String()
 
+    #: The data source to be instantiated. Define this to your DataSource
+    data_source_class = Type(BaseDataSource)
+
+    #: The model associated to the data source.
+    #: Define this to your DataSourceModel
+    model_class = Type(BaseDataSourceModel)
+
     #: Reference to the plugin that carries this factory
+    #: This is automatically set by the system. you should not define it
+    #: in your subclass.
     plugin = Instance(Plugin)
 
     def __init__(self, plugin, *args, **kwargs):
         self.plugin = plugin
         super(BaseDataSourceFactory, self).__init__(*args, **kwargs)
 
-    @abc.abstractmethod
     def create_data_source(self):
         """Factory method.
         Must return the factory-specific BaseDataSource instance.
@@ -36,8 +48,15 @@ class BaseDataSourceFactory(ABCHasStrictTraits):
         BaseDataSource
             The specific instance of the generated DataSource
         """
+        if self.data_source_class is None:
+            msg = ("data_source_class cannot be None in {}. Either define "
+                   "data_source_class or reimplement create_data_source on "
+                   "your factory class.".format(self.__class__.__name__))
+            log.error(msg)
+            raise RuntimeError(msg)
+
+        return self.data_source_class(self)
 
-    @abc.abstractmethod
     def create_model(self, model_data=None):
         """Factory method.
         Creates the model object (or network of model objects) of the KPI
@@ -55,3 +74,14 @@ class BaseDataSourceFactory(ABCHasStrictTraits):
         BaseDataSourceModel
             The model
         """
+        if model_data is None:
+            model_data = {}
+
+        if self.model_class is None:
+            msg = ("model_class cannot be None in {}. Either define "
+                   "model_class or reimplement create_model on your "
+                   "factory class.".format(self.__class__.__name__))
+            log.error(msg)
+            raise RuntimeError(msg)
+
+        return self.model_class(self, **model_data)