TechTreeTrait system has been made

Techlevel UI added
TechLevel UI hidden when no techlevels in mod\nTechlevel dropdown button disabled if only one option

You can make new tech levels with ProvidesTechPrerequisite@TechLevel5:
the ~ annotation hides the item from build queue if prerequisite is not met

Also reworked most of the prereq system so its more flexible and allows a lot of interesting things