Show upcoming jobs on the dashboard

On the dashboard:
- adds a new ‘in the next 24 hours’ section to the dashboard which lists
  upcoming jobs
- tweaks some spacing on the dashboard so that it doesn’t look like too
  much of a mess
- don’t show scheduled jobs in the table of normal jobs

On the jobs page:
- don’t show scheduled jobs

app/assets/stylesheets/components/big-number.scss

@@ -40,7 +40,7 @@
 
   @extend %big-number;
   position: relative;
-  margin-bottom: $gutter-half;
+  margin-bottom: $gutter-two-thirds;
 
   .big-number {
     padding: $gutter-half;

app/assets/stylesheets/components/show-more.scss

@@ -1,3 +1,4 @@
+%show-more,
 .show-more {
 
   @include core-16;
@@ -8,7 +9,7 @@
   border-top: 1px solid $border-colour;
 
   &:focus {
-    
+
     outline: none;
     color: $text-colour;
     box-shadow: 0 -10px 0 0 $yellow;
@@ -32,3 +33,8 @@
   }
 
 }
+
+.show-more-empty {
+  @extend %show-more;
+  margin-top: -10px;
+}

app/assets/stylesheets/components/table.scss

@@ -10,11 +10,20 @@
 
 .dashboard-table {
 
+  .heading-medium {
+    margin-bottom: 5px;
+  }
+
   .table {
     table-layout: fixed;
   }
 
-  .table-field-headings,
+  .table-field-headings {
+    th {
+      font-size: 0;
+    }
+  }
+
   .table-field-headings-visible {
     th {
       padding-bottom: 5px;