Remove lv, mv, and hv tiers from power tools.
Theyre already tiered with Mk1-3 (at least drill is, more in the future).
Tools can be considered as designed for different tiers of circuits thx to their power needs.
For example Mk3 will require ages to load in LV batbox.
Batboxes load tools timining: LV standard (1000EU), MV 4x faster (4000EU), HV 16x faster (16000EU)
Also since 1EU is the same in any circuit it is possible to move energy from one to another with portable devices like crystals.

Other changes:
- moved charge/discharge functions to battery_boxes_commons.lua
- added UI style backgrounds for all the batboxes