Make cooldown for hopping interfaces/machines configurable

And also decrease the default cooldowns.

Config example:
cooldownFluid: Number of ticks between each import/export action for
Fluids, i.e. 0 => 1 Bucket per tick, 20 => 1 Bucket per Second.

Defaults at the moment:
* Flux: 0, i.e. 10000 RF/t throughput
* Fluids: 10, i.e. 2 Buckets per second
* Items: 10, i.e. 2 Stacks per second

Should fix bug 1 of #19