Changes:

- the clock keybinding got replaced with a clock item

- add an optional toggle to make the digital clock 12-hour instead of 24-hour. Apparently some people like that.

- entities can swim in fluids

- lava damages entities

- player gets damaged after loosing all oxygen (drowning)

- screen becomes a bit red when taking damage

- added beds. You can right-click them to skip about 12 hours pretty much instantly

- improved the performance by moving light updates to a separate thread

- reworked the item selection window. Now it has categories you can choose from.