New 33m pool size

I have been asked a couple of times to add the 33m pool length. This has now been added.

I have also added the functionality for you to be able to delete swim events (25m, 50m, 100m etc). When you are on the events page, click on one and if you have not used that event on a swim time, a delete option will be visible.

This is useful if you have made a mistake or want to delete an event etc.