tweaks/expands shield gen supply packs

Signed-off-by: Cael Aislinn <cael_aislinn@yahoo.com.au>
misc tweaks and cleanups to shield gens/caps (renames, power usage), added a temp recharge delay when a field takes damage

Signed-off-by: Cael Aislinn <cael_aislinn@yahoo.com.au>
Merge pull request #4792 from caelaislinn/shieldgens

Shield generators update