Add "Complete task" functionality

Now tasks can be completed by the user right from within the main page.

Signed-off-by: Emanuele <feliziani.emanuele@gmail.com>
Add html escaping

Add html escaping via Rack::Utils and escape the content when displayed. Sql injection is not a problem because DataMapper handles that for us when using DataMapper built-in methods.

Signed-off-by: Emanuele <feliziani.emanuele@gmail.com>