Issue description:
Powercell cost factor is currently not taken into effect when subtracting from the internal buffer (changed in the following commit: 0f1aad4)

The effect of this is that the cells no longer cost any RF to transfer between dimensions or across large gaps, the only effect is that the RF/t is slightly lower when the energy cell gets low because the RF/t calculation does use the cost factor. (Note that this means that if you try to entirely drain the network with a cost factor, it will be unable to drain the last 1RF because any cost makes the integer division for RF/t go to 0)

Steps to reproduce:

• Place down 2 energy cells, link together
• Fill the cells
• Take one cell to the nether, leaving the other in the overworld (easiest way to get max range)
• Place cell down, output to an unlinked cell, wait for unlinked cell to fill
• Energy left in linked cell is exactly 50%, though the cost should make it lower

Versions:

• Minecraft: 1.12.2
• Forge: 14.23.2.2611
• McJtyLib: 2.6.5
• RFTools: 7.30
• JEI: 4.8.5.147
• RedstoneFlux: 2.0.1.2
• TheOneProbe: 1.4.19
• WeirdingGadget: 2.0.5