[Datahub] : Footer

[cmoinier]

This PR adds the footer to the MEL datahub pages.

The footer is very similar to the one at https://www.lillemetropole.fr/ .
The differences are :

• The 'Contactez-nous' button doesn't link to the MEL page, but emails to a specified hard-coded address.
• The partners icons are different (asked by client), and the original text and icon are removed (the render is different from the mockups)
• The cookies tab is gone.

[tkohr]

Thanks for the nice footer @cmoinier !

I'm just noticing two things when testing:

• The footer appears much higher than on https://www.lillemetropole.fr and even identical logos (like social media) appear bigger. I think decreasing the size of the two centered logos would also help decreasing the height at the same time.
• When loading the app, the footer appears quickly because the page content has not fully loaded yet. Maybe we could improve this behavior somehow (perhaps with a min-heigth somewhere).

[Angi-Kinas]

Thanks @cmoinier, this looks good already!

I have some comments about the styling but some of them are personal preference.
The main thing I noticed are the effects on the icons as well as the links at the bottom that are missing. Also important are the translations for the text that should be added to the translation files.
Let me know if something is not clear.

[Angi-Kinas]

Thanks @cmoinier for addressing all the comments. For me this looks good to be merged :)

Two last things I would implement:

• underline icons on hover
• height of footer in responsive view

[tkohr]

Thanks, @cmoinier, looks really nice now! Just left a last suggestion for the padding.