Enable testing of MongoEngine backend on Python 3

Fixed bs4 modal details/edit view markup

Replace bootstrap3 "well" class with bootstrap4 "card"

Update import location for SQLAlchemy project reorganization.

Add try/except handler for handling imports from different SQLAlchemy project versions.

Update import location for new SQLAlchemy version.

fix broken styling in datepicker

See https://stackoverflow.com/a/38622102

Update requirements-dev.txt

Bootstrap4 Work-In-Progress

Fixed file upload field markup for bs4

fix: Correct styling issues

Bootstrap4 ui fixes

Minor UI fixes

fix: Correct navbar styling issue

Add a hook for custom SQLAlchemy model initializers (#1927)