Feature recurring events

This feature had started to be worked on last fall, and somehow the table creation sql for `global_lu_restricted_days` didn't make it into the install sql, but is in the 1600 upgrade entrada.sql file. So, if you don't have that table already, go into either the 1600 upgrade sql, or search for the `global_lu_restricted_days` file in the install entrada.sql file and add it from there, as I didn't want to duplicate table creation in the upgrade scripts.

Any feedback regarding the interfaces or this functionality would be greatly appreciated. The majority of the changes fall under Admin->System Settings->Manage Organisation->Restricted Days (where you set what days the system will notify you of if you have recurring events on, such as weekends or holidays, to hopefully prevent accidental scheduling on days when it isn't valid to run sessions), and Admin->Manage Events-> Add/Edit/Content, as well as a new page in there which lists the recurring events related to the current event, and has been added as a new "tab" on the manage event pages.