[DIFE-239] navbar: overwrite menu items

• Remove Home Button

The navbar items:

• About the Conference [link to /pages/about] 
• Topics [link to /processes] -> if published participatory process
• Events [link to /meetings] 
• Plenaries [link to an external url] 
• Citizens panels [link to /assemblies] -> if published assemblies

The menu item labels can be translated in config/locales/*.yml, the About the Conference label will be the translated page title:

en:
  decidim:
    menu_overwrite:
      citizens_panels: Citizens panels
      events: Events
      plenaries: Plenaries
      topics: Topics