Redo line-height globally

- Rename -height to -height-base to match other vars
- Drop use of -height across the board and rely on it to be inherited
- Adjust padding of .dropdown-header to account for different line-height of h6 heading element (this needs refactoring for variables and rems also)

scss/mixins/_pagination.scss

@@ -4,7 +4,6 @@
   .page-link {
     padding: $padding-y $padding-x;
     font-size: $font-size;
-    line-height: $line-height;
   }
 
   .page-item {