Don't disable existing loggers when Alembic runs (#65)

Python's documentation about this
https://docs.python.org/3/library/logging.config.html#logging.config.fileConfig.
Alembic auto-generates this file, but I can't find other uses of it in
Suffolk code (@nonprofittechy, I suggest you check LemmaLegal packages).

Found by finding that when logs were broken on servers (the prod and
sometimes dev servers), `docassemble.webapps.server.sys_log.disabled ==
True`. Consulted https://stackoverflow.com/a/43279730/11416267 once I
discovered that.

Tested and confirmed fixed locally on a localhost docassemble with the
following (no good unit test :

* restart docassemble's python code (by saving the config and restarting
the server)
* confirm the logs work by loading an interview with a unique log
message, checking it's timestamp
* run the `GithubFeedbackForm/feedback.yml` interview
    * on older versions, no more logs will be output after that
* on this fixed version, you should be able to trigger and see new logs

Author: BryceStevenWilley

docassemble/GithubFeedbackForm/alembic/env.py

@@ -17,7 +17,7 @@
 # Interpret the config file for Python logging.
 # This line sets up loggers basically.
 if config.config_file_name is not None:
-    fileConfig(config.config_file_name)
+    fileConfig(config.config_file_name, disable_existing_loggers=False)
 
 # add your model's MetaData object here
 # for 'autogenerate' support