updated en-GB.com_jevents.ini to include difficulty language settings
Update config.xml

Rearranged and updated to include difficulty attribute
Update eventsadmin.css

updated to hide fields marked with hiddenDifficulty
edit.php 

Updated to mark the class of each field and fieldset with hiddenDifficulty if its difficulty attribute is greater than the current selected difficulty.
Merge pull request #59 from owendp/master

Adds difficulty level to the JEvents configuration menu