Simple script to add Responsable and BRN users

CLI script invoked with role and CSV file, with usage message.
Passwords have to be put in the CSV file (-> secure passwords shall not
be used). It could drastically be improved, but this is simple and
convenient. A future update may feature the use of flask-security.
Support for multiple Activites per Responsable

With ability to add, display, edit and delete them.
An Activite can be added only if they're all fully configured
First draft of BRN pages
Better new Activite handling

No creation before data is filled -> no need to handle incomplete
Activites
Style: setup bootstrap + small config
Remove messages, superseeded by flashes
Activite template fix
Updated models: Planning support
Requires_roles call login_required

Therefore there is no need to decorate a function with login_required
when it has requires_roles.

views.brn imports got cleaned at this occasion.