Upgrade LEAN Python to 3.6 from 2.7

- Adds log to display the python version the algorithm is using.
- Fixes python algorithms that were failing because of small subtleties
like leading zeroes.
- Updates pythonnet with a version compiled with python 3.6 flags

- Changes in DockerfileFoundation: we now use miniconda to manage the python
environment.
- Took the opportunity to add NTLK (#1349), Tensorforce (#1369) and
PyTorch/Pyro (#1385).
- Changes readme in Algorithm.Python to show steps to install miniconda

Algorithm.Python/DropboxBaseDataUniverseSelectionAlgorithm.py

@@ -59,7 +59,7 @@ class DropboxBaseDataUniverseSelectionAlgorithm(QCAlgorithm):
     def OnData(self, slice):
 
         if slice.Bars.Count == 0: return
-        if self._changes == SecurityChanges.None: return
+        if self._changes == None: return
         
         # start fresh
         self.Liquidate()
@@ -69,7 +69,7 @@ class DropboxBaseDataUniverseSelectionAlgorithm(QCAlgorithm):
             self.SetHoldings(tradeBar.Symbol, percentage)
         
         # reset changes
-        self._changes = SecurityChanges.None
+        self._changes = None
     
     def OnSecuritiesChanged(self, changes):
         self._changes = changes