New package 'lib' for modules without dependencies

- filters, mail, ucsv and upload barely import anything[0] that's not
  included with python
- they've been moved in lib/
- models was a candidate for this change too, but it's only
  project-specific data and not at lib at all, so it would not have made
  sense
- lib.mail.mail has been imported in lib/__init__ to make it more
  elegant
- the imports in the project have been updated
- the goal was to clean the root directory

0: upload uses werkzeug.secure_filename
Templates: removed footer
Templates: fixed static js resources URL
Fixed url of a view
Activites list: fixed SQL query
Models: fixed SQLAlchemy query
Template: fixed typo
Better model Enum handling
Tools file