[Fix] Stereochemistry prediction handling (#228 and #238) (#250)

**This pull request will need a separate migration pull-request**

I have added an alert box in two places when the user tries to predict with stereo chemistry.

When a user predicts a pathway with stereo chemistry an alert box is shown in that node's hover.
To do this I added two new fields. Pathway now has a "predicted" BooleanField indicating whether it was predicted or not. It is set to True if the pathway mode for prediction is "predict" or "incremental" and False if it is "build". I think it is a flag that could be useful in the future, perhaps for analysing how many predicted pathways are in enviPath?
Node now has a `stereo_removed` BooleanField which is set to True if the Node's parent Pathways has "predicted" as true and the node SMILES has stereochemistry.
<img width="500" alt="{927AC9FF-DBC9-4A19-9E6E-0EDD3B08C7AC}.png" src="attachments/69ea29bc-c2d2-4cd2-8e98-aae5c5737f69">

When a user does a prediction on a model's page it shows at the top of the list. This did not require any new fields as the entered SMILES does not get saved anywhere.
<img width="500" alt="{BED66F12-5F07-419E-AAA6-FE1FE5B4F266}.png" src="attachments/5fcc3a9b-4d1a-4e48-acac-76b7571f6507">

I think the alert box is an alright solution but if you have a great idea for something that looks/fits better please change it or let me know.

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#250
Co-authored-by: Liam Brydon <lbry121@aucklanduni.ac.nz>
Co-committed-by: Liam Brydon <lbry121@aucklanduni.ac.nz>

utilities/chem.py

@@ -81,6 +81,10 @@ class FormatConverter(object):
     def formula(smiles):
         return Chem.rdMolDescriptors.CalcMolFormula(FormatConverter.from_smiles(smiles))
 
+    @staticmethod
+    def has_stereo(smiles):
+        return "@" in smiles or "/" in smiles or "\\" in smiles
+
     @staticmethod
     def from_smiles(smiles):
         return Chem.MolFromSmiles(smiles)