Display error when trying to encrypt folder/DayOne journal types (#1315)

* Raise exception when trying to commit folder-based journal (including DayOne)
* Add test to ensure this doesn't mess with encrypting normal journals
* Consolidate and standardized tests

jrnl/FolderJournal.py

@@ -25,6 +25,7 @@ class Folder(Journal.Journal):
     def __init__(self, **kwargs):
         self.entries = []
         self._diff_entry_dates = []
+        self.can_be_encrypted = False
         super(Folder, self).__init__(**kwargs)
 
     def open(self):