Fixes #7283: using translate directive in <span> to avoid infinite loop.

Changing this table header to use a child <span> with the translate
directive thus avoiding an infinite loop created by the interaction
between the translate and sortable directives.

http://projects.theforeman.org/issues/7283
Merge pull request #4621 from waldenraines/7283

Fixes #7283: using translate directive in <span> to avoid infinite loop.