Simplify using text color for links

Using `inherit` is IMHO more expressive since it means "use the color of
the parent element".

This is particularly useful for CONSUL installations using custom
styles. Consider the following code:

```
h2 {
  color: $white;

  a {
    color: $white;
  }
}
```

If we'd like to customize the way headings look, we'd have to override
two colors:

```
h2 {
  color: $red;

  a {
    color: $red;
  }
}
```

Consider the scenario where we use `inherit`:

```
h2 {
  color: $white;

  a {
    color: inherit;
  }
}
```

Now we only need to override one color to change the styles:

```
h2 {
  color: $red;
}
```

app/assets/stylesheets/legislation.scss

@@ -57,7 +57,7 @@
   }
 
   h3 a {
-    color: $black;
+    color: inherit;
     margin-bottom: 1rem;
   }
 }