New monster pages, item descriptions on hover, sign-up changes

Changes

• Database: monster pages have a new look: big picture, stats, damage by element, drops with real rates and the maps they live on.
• Database: item pictures now show their description when you hover them (tap on a phone), also in a monster's drop list on a map page.
• Register and pre-register: if you are already logged in, you now see your account instead of the sign-up form.
• Sign-up: a new optional question, "Where did you hear about us?", helps us see which links bring players.