enhanced update script (issue #588)
altered categories model + view (frontend) (issue #588)
- new param showemptycats, params re-ordered
- new text ids COM_JEM_SHOWEMPTYCATS(DESC) (admin lang file)
- adapted update script
- added div (clr) to ensure buttons not mixed with content (issue #581 related)
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Merge branch 'jemproject-master'

Conflicts:
	site/views/categories/tmpl/default_table.php
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Merge branch 'develop' into feature/page-heading

Conflicts:
	site/views/categories/tmpl/default_table.php