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

technic/tools/chainsaw.lua

@@ -3,7 +3,7 @@ local chainsaw_max_charge      = 30000 -- 30000 - Maximum charge of the saw
 local chainsaw_charge_per_node = 12    -- 12    - Gives 2500 nodes on a single charge (about 50 complete normal trees)
 local chainsaw_leaves          = true  -- true  - Cut down entire trees, leaves and all
 
-technic.register_LV_power_tool ("technic:chainsaw",chainsaw_max_charge)
+technic.register_power_tool ("technic:chainsaw",chainsaw_max_charge)
 
 minetest.register_tool("technic:chainsaw", {
         description = "Chainsaw",

technic/tools/flashlight.lua

@@ -1,7 +1,7 @@
 -- original code comes from walkin_light mod by Echo http://minetest.net/forum/viewtopic.php?id=2621
 
 local flashlight_max_charge=30000
-technic.register_LV_power_tool ("technic:flashlight",flashlight_max_charge)
+technic.register_power_tool ("technic:flashlight",flashlight_max_charge)
       
 minetest.register_tool("technic:flashlight", {
 	description = "Flashlight",

technic/tools/mining_drill.lua

@@ -210,7 +210,7 @@ function drill_dig_it4 (pos,player)
 	drill_dig_it0 (pos,player)
 end
 
-technic.register_MV_power_tool ("technic:mining_drill",mining_drill_max_charge)
+technic.register_power_tool ("technic:mining_drill",mining_drill_max_charge)
 minetest.register_tool("technic:mining_drill", {
 	description = "Mining Drill Mk1",
 	inventory_image = "technic_mining_drill.png",
@@ -243,10 +243,10 @@ minetest.register_tool("technic:mining_drill_mk2", {
 	return itemstack
 	end,
 })
-technic.register_HV_power_tool ("technic:mining_drill_mk2",mining_drill_mk2_max_charge)
+technic.register_power_tool ("technic:mining_drill_mk2",mining_drill_mk2_max_charge)
 
 for i=1,4,1 do
-technic.register_HV_power_tool ("technic:mining_drill_mk2_"..i,mining_drill_mk2_max_charge)
+technic.register_power_tool ("technic:mining_drill_mk2_"..i,mining_drill_mk2_max_charge)
 minetest.register_tool("technic:mining_drill_mk2_"..i, {
 	description = "Mining Drill Mk2 in Mode "..i,
 	inventory_image = "technic_mining_drill_mk2.png^technic_tool_mode"..i..".png",
@@ -267,10 +267,10 @@ minetest.register_tool("technic:mining_drill_mk3", {
 	return itemstack
 	end,
 })
-technic.register_HV_power_tool ("technic:mining_drill_mk3",mining_drill_mk3_max_charge)
+technic.register_power_tool ("technic:mining_drill_mk3",mining_drill_mk3_max_charge)
 
 for i=1,5,1 do
-technic.register_HV_power_tool ("technic:mining_drill_mk3_"..i,mining_drill_mk3_max_charge)
+technic.register_power_tool ("technic:mining_drill_mk3_"..i,mining_drill_mk3_max_charge)
 minetest.register_tool("technic:mining_drill_mk3_"..i, {
 	description = "Mining Drill Mk3 in Mode "..i,
 	inventory_image = "technic_mining_drill_mk3.png^technic_tool_mode"..i..".png",

technic/tools/mining_laser_mk1.lua

@@ -1,5 +1,5 @@
 local laser_mk1_max_charge=40000
-technic.register_LV_power_tool ("technic:laser_mk1",laser_mk1_max_charge)
+technic.register_power_tool ("technic:laser_mk1",laser_mk1_max_charge)
 
 local laser_shoot = function(itemstack, player, pointed_thing)
 				local laser_straight_mode=0

technic/tools/sonic_screwdriver.lua

@@ -1,5 +1,5 @@
 local sonic_screwdriver_max_charge=15000
-technic.register_HV_power_tool ("technic:sonic_screwdriver",sonic_screwdriver_max_charge)
+technic.register_power_tool ("technic:sonic_screwdriver",sonic_screwdriver_max_charge)
 
 minetest.register_tool("technic:sonic_screwdriver", {
 			description = "Sonic Screwdriver",