Theme update (#553)

* Start to update the theme

- Ligther colors
- No more border radius
- Buttons are now always colored
- Start to redesign the post page (according to the Figma mockups)

* Fix build script: it now recompiles everytime a scss file changed

* Make sure the article illustrations are not too big

* Make articles wider (70 characters)

* Better contrast between gray shades

* Various improvements

* Better mobile style

* New style for the footer

* Improve comment style

* Better responsiveness again

* Limit the size of the article cover

* Last details?

- Improve buttons on the media page
- Improve lists

* Pin the stdweb version that we use

It changed because I removed Cargo.lock to handle a merge conflict

I could have updated cargo web too, but it mean I should have re-built
the CI docker image and it was taking forever.

* Better contrast for links in the header of the article

* Add a basic privacy policy

* Remove "also"

* Fix a few issues

- Don't watch static/css in build.rs
- Another shade of white
- Remove useless margin rule for error messages

templates/medias/index.rs.html

@@ -15,7 +15,7 @@
         <p>@i18n!(ctx.1, "You don't have any media yet.")</p>
     }
 
-    <div class="cards spaced">
+    <div class="cards">
         @for media in medias {
           <div class="card">
               <div class="cover media-preview @media.category().to_string()"