General visual adjustment

[hofmannv]

• [x] remove inactive menu from HMC webpage
• [x] add aheader picture
• [x] add a survey-dashboard logo
• [x] adjust fonts, colors according tho HMC CI

[SilkeGerlich]

@hofmannv

Where can I find the header picture and the logo?

[hofmannv]

• we can either use the one from hub matters dashboard or create an own one.
• a logo does not yet exist

[hofmannv]

banner: https://fairdashboard.helmholtz-metadaten.de/assets/Banner.png

[SilkeGerlich]

Done