Add row numbers to tables

When a table is showing the contents of a CSV file, it should look
something like a spreadsheet.

The minimally skeuomorphic way to do this is by adding row numbers.

This commit doesn’t
- make the row numbers monospace (it’s barely noticeable and doesn’t
  reflect what actual spreadsheets do)
- make the first column heading ‘Row’ (again, doesn’t reflect how actual
  spreadsheets work, and takes up more valuable space)

app/templates/views/styleguide.html

@@ -178,7 +178,7 @@
         {% endcall %}
       {% endcall %}
 
-      {% call(item) list_table(
+      {% call(item, row_number) list_table(
         [
           {
             'file': 'dispatch_20151114.csv', 'status': 'Queued'
@@ -206,7 +206,7 @@
         {% endcall %}
       {% endcall %}
 
-      {% call(item) list_table(
+      {% call(item, row_number) list_table(
         [],
         caption='Jobs',
         field_headings=['Job', 'Time'],