Several theme changes (#659)

* Several theme changes

- Add max width of 1440px
- Rename css file
- Fix edit button
- Add local Roboto font

Signed-off-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>

docs/mkdocs.yml

@@ -4,6 +4,7 @@ repo_url: https://github.com/hedgedoc/hedgedoc
 site_description: 'HedgeDoc Documentation'
 site_author: 'HedgeDoc Developers'
 docs_dir: content
+edit_uri: https://github.com/hedgedoc/hedgedoc/edit/master/docs/content/
 nav:
   - Home: index.md
   - Installation:
@@ -56,6 +57,8 @@ theme:
     - navigation.tabs
     - navigation.sections
     - toc.integrate
+  font: false
 
 extra_css:
-  - theme/styles/hedgedoc-color.css
+  - theme/styles/hedgedoc-custom.css
+  - theme/styles/roboto.css