Increase event description limit

[chapoi]

@Lou

The main problem for me is that when a user adds an event description, there is a silent failure. When description holds > 1000 characters, the event database record does not seem to be created. The text is still in the topic within the [event] block, but the event itself is not visible anywhere to users.

Coincidentally, this has just been reported as a bug report Event silently fails if description is longer than 1000 characters