!!!Add an "Event Handler" API to JSPWiki

There are 3 basic types of events on a Wiki page:
* __Create__ A new page has been created.
* __Read__ Someone entered a page
* __Modify__ someone edited a page.

The idea is that when one of these happens, a list of "event handlers" get invoked. An event handler is a class that implements a perticular interface (just like AWT event handlers). The engine passes an event object containing all there is to know about the event.

Now, where do these handlers come from? Well, they are listed in a jspwiki.events.properties file. So, a site manager can define her own handlers, put them under WEB-INF/classes, and add them to the list.

Using this, anyone can contribute implementations for email notification, statistics, content verification (e.g. - scan for viruses) etc.

We could also consider other events, like:
* User Events
** new user
** user loged in
** user loged out
* [Comment |CommentingIdeas] events
** comment added
** etc.
* etc.

- YishayMor

Yes, I was thinking about something like this, but not so general.  See [PageFilters] for more discussion.

-- JanneJalkanen