Refactor core and base classes (#931)

* Improve the NWIndex class
* Improve the NWItem and NWDoc classes
* Make some optimisations in projects and update tests
* Minor changes to string formatting in main source file
* Add some more protection to core classes
* Make all converter class attributes private

novelwriter/core/spellcheck.py

@@ -25,7 +25,6 @@ along with this program. If not, see <https://www.gnu.org/licenses/>.
 
 import os
 import logging
-import novelwriter
 
 from novelwriter.error import logException
 
@@ -36,8 +35,6 @@ class NWSpellEnchant():
 
     def __init__(self):
 
-        self.mainConf = novelwriter.CONFIG
-
         self._theDict = None
         self._projDict = set()
         self._projectDict = None