shield extension names

Just to put them in line with the naming scheme of other extensions.

efficient
shield - reduces the reactor usage
all other extensions - reduces the accumulator usage

optimized
shield - reduces the accumulator usage
all other extensions - reduces the CPU usage

economical
shield - no extension
all other extensions - reduces the reactor usage

I think the shield extension names should look like this to make things more in line and easier to remember what they do:

Efficient shield usage -> Economical shield usage
Optimized shield usage -> Efficient shield usage