changed css classes to differ between event-list-view and single-event-view (Issue #28)

also added additional div container around complete eventlist output
added tooltip texts for the widget options (Issue #26)
removed escaped quotes in info message after adding/editing an event (Issue #27)
moved admin about page to seperate file/class
whitespace fixes
moved admin settings page to seperate file/class
moved admin new event page to seperate file/class
moved admin main page to seperate file/class
added missing permission check for new event and about page
changed admin class to a singleton; added admin init function
avoid loading all admin site classes; changed some function names
restructure of admin settings class
improved deleted category message
moved missing part of category table to the propriate function
added possibility to edit existing categories (Issue #13)
do not change publish date and user when an event is modified (Issue #29)
small code improvements
preparation for version 0.4.3
Merge branch 'develop'