Cleanup: Dependency Management

No longer redistribute BuildCraft, IndustrialCraft 2 ->
now fetched via gradle from the correspondig maven repo
Added new PowerSystem: GregTech

Some details:
 - Each Voltage Tier has its own Consumer/Producer (like IC2)
 - The Consumer will only consume 'full' Packets (1 Amp), no energy gets 'wasted'
 - The Producer generates 1A, this applies to all tiers
 - Current Balancing is based upon IC2 so 32EU @1A are equal to 32EU from IC2
 - You may want to increase the Bridge Buffer Size in your Configuration
   As GregTech has Higher Voltage Tiers than 60k EU@1A
   (ZPMV: 128k, UV 512k - EU @1A)