Restructure header navbar to fit elements on all screens

• Remove icons to reduce required amount of space
• Remove home button since it is redundant to clicking on the logo. I would assume this behavior is commonly known. It frees up some space.
• Make the hamburger button appear already on tablet-sized screens

@jandt-desy Could you please check, if the changed layout would be okay for you?

Closes #5 (closed)

_data/navigation.yml

@@ -11,37 +11,26 @@
 # original Markdown.
 
 header:
-        - title: Home
-          url: /
-          fontawesome_class: "fas fa-home"
-
         - title: News
           url: blog/
-          fontawesome_class: "fas fa-rss"
 
         - title: Services
           url: "/"
-          fontawesome_class: "fas fa-list"
 
         - title: Mission
           url: "/"
-          fontawesome_class: "fas fa-bolt"
 
         - title: Roadmap
           url: "/"
-          fontawesome_class: "fas fa-map-signs"
 
         - title: International
           url: "/"
-          fontawesome_class: "fas fa-globe-europe"
 
         - title: Contact
           url: "contact"
-          fontawesome_class: "fas fa-envelope"
 
         - title: Jobs
           url: "/"
-          fontawesome_class: "fas fa-user"
 
 footer:
          - title: Contact