Migrate requirements to udata 3

[maudetes]

Use udata 3 requirements and add a default front plugin using gouvfr front.

Fix all requirements update:

• close https://github.com/opendatateam/docker-udata/pull/262
• close https://github.com/opendatateam/docker-udata/pull/260
• close https://github.com/opendatateam/docker-udata/pull/256
• close https://github.com/opendatateam/docker-udata/pull/255
• close https://github.com/opendatateam/docker-udata/pull/253
• close https://github.com/opendatateam/docker-udata/pull/250