Move to Bootstrap 4.0

[netsensei]

Detailed description

Bootstrap 3.3.7 is currently used to drive the (primitive) interface. However, Bootstrap 4.0 is the new stable version. Since the interface is still fairly uncomplicated, now's the chance to upgrade to Bootstrap 4.0.

Context

This change is important to ensure the longevity and the maintenance of the project. While Bootstrap 3.3.7 certainly has it merits, it's better to go with the latest major stable release while there's still a window of opportunity to do so.

If we stay with 3.3.7 and develop a more advanced interface - pending certain requests - it will be harder to move to 4.x and later major versions.

Possible implementation

• Switch out bootstrap-sass for the bootstrap package
• Rebuild the templates using bootstrap 4.0 templates.

The latter change is due anyhow since the original templates where conceived within a very limited scope.