Clean up equipment-related code from the core

Now that equipment is managed by Lua, a lot of the code from EquipType.h is unnecessary. The set of commodities (cargo types) is currently still needed in the core, because system generation includes code to pick the trade balance/price adjustment for different commodities, and illegal goods are currently still managed by C++ code.

This patch set does various bits of minor clean-up, and then removes EquipType.{h,cpp}. The commodity type enum and commodity information (base price, etc) are moved to src/galaxy/Economy.{h,cpp}. Equipment types and data, equipment slots, and data about different laser types are all removed, since they are no longer needed.

I have not yet confirmed that sysgen produces the same output (as it should) after this patch. I think I need to add code to include trade level data in the system data dump.