Bride-of-frankensystem

This is the last release of the 1.x version. Future releases will not support Python 2.7.x.

Changes/Enhancements:
* Flag some parts of the questionnaire JSON as safe (so HTML can be added to those fields).
* Custom export feature now works without grouping or ordering variables.
* Can now group by multiple columns on custom exports.
* Added a simple honeypot to the consent page.
* Added a progress summary to the top of the admin panel's progress page.
* When assigning conditions to participants, omit "abandoned" attempts from the calculation of participant counts in each condition.
* Added in the ability to load in participant progress based on their MTurk ID (via the `RETRIEVE_SESSIONS` config option, set it to `True`).
* Removed the IP address check on verify_session_valid.
* Made changes to work with the 2021.1.x version of Unity (which uses a different type of compression).
* Added a method of defining database tables via a JSON file instead of in the `models.py` file.

Fixes:
* Fixed variance fallback method.
* Fixed bug where the last condition's questionnaires weren't found.
* Possible fix for participants getting redirected back to the start_mturk page.

Features Added
* Session information from previous attempts can now be loaded in after entering the MTurkID.
* Questionnaire calculation strings that can be embeded into the .json files and are exported by /admin/export (e.g., for subscales)

General Improvements
* condition field is now nullable
* added config option to allow/restrict re-takes (multiple attempts)
* added crumbs variable to be added to templates by default
* pages with blank names no longer show in the bread crumb list
* admin panel: if logGridClicks is False, don't show dropdown
* Server-side sessions are now provided by a custom interface, rather than flask-sessionstore.
* Removing dependency on Flask-SocketIO (while allowing eventlet to stay)
* Slight change to how blueprints are imported.
* Embedded js libraries into project rather than linking to external URLs.
* Additional admin pages can now be defined directly in blueprints, rather than just in the config file.
* Logging of grid click data is now working again
* Added check on /current_url route to avoid exceptions for people who have no session data.
* Fixed previewing questionnaires not loaded in the config.
* Now reports the URL when running with `self.debug = False` (on launch)
* Fixed a bug with condition assignment.
* Added basic /submit route that redirects user on form submission.
* blank logo (instead of USask logo)
* Updated README.md and setup.py