Release alpha v0.5.1

Day/night Cycle
- It is in test phase, any feedback is welcome
Fixed bugs
- Hidden building ~statue~ is now still hidden when selecting "show all unlocked buildings".
- Tooltip is no longer behind the menus (now it is)
- You can now get the advanced multicourt
- Now you can get the coastal tourist district
- when saving, the text popup "there is only one save slot" does not appear any more
Mechanics
- Car parks are no longer converted into abandoned buildings. They are now replaced by other houses.
- Proto-warehouses produce the same as warehouses, so you don't have to wait for them to be built before you can build industries.
- The intelligence of the cars has been improved a bit.
Balance
- Houses demand less density in the archipelago biome, as it is more difficult to obtain large residential areas.
Graphics
- Zooming is now more fluid
- long city name now does not word wrap
- Exiting the game asks "save game?"
- There are now bushes and mushrooms in the forests.