Fix powerbanks losing all power when placed when using technic mod.

[olivia-may]

Powerbanks would charge in a battery, then when you go place them, they frustratingly would reset to 0 power. This was because the old set_charge and get_charge functions (the ones used for technic, NOT technic plus) would always return 0. I fixed this by copying the default_set_charge and default_get_charge functions from technic's technic/machines/register/battery_box.lua file. Now it works as intended.

I also added a second, optional commit, that makes the "Remaining Charge: ..." part of the formspec more easily visible. Sometimes the number gets cut off, especially on smaller screens.

[OgelGames]

Sorry for the delay on this, it should be fixed now.