Various improvements and fixes

[JordiVanOs]

Adds link to the admin panel for admins
Adds link for division contacts to admin panel
Adds restrict (read only) access to members for division contacts within their division
Improves styling
Updates logo
Improves mobile responsiveness
Removes legacy division overview (/groep/)

[Nowa-Ammerlaan]

I'm getting:

An exception has been thrown during the rendering of a template ("Could not find the entrypoints file from Webpack: the file "/var/www/project/public/assets/entrypoints.json" does not exist.").

[Xesau]

Run yarn dev of yarn build to generate the entrypoints.json file

[Nowa-Ammerlaan]

That fixed it.

Some minor comments:

• please update readme with new login info for admindebaas
• if this yarn build is going to be always required to get this up and running, please add this step to readme as well.
• and finally:
  
  I am personally not fond of this blue in our red colour scheme. Can we make this black instead?