Added collection factor to AntimatterCollector

To make a bigger antimatter collector, you can create a new part, that
has multiple MODULE elements.
Unfortunately the game will freeze, when you try to add thousands of
MODULE elements.
The game will also be unplayable when you try to build a craft with
thousands of AntimatterCollectors.
Therefore I suggest adding a collection factor to the MODULE which would
look like this in the part.cfg:
MODULE
{
name = AntimatterCollector
collectionFactor = 10
}
So I suggest a factor of 10 for doubling the diameter of the collector
while it's volume increases 8 times.
Now, one could create an entire collector family:
Diameter mg/d mg/s   Weight
2.5        4   0.0000462963    4
5       40   0.000462963   12
10      400   0.004629630   36
20     4000   0.046296296  108
40    40000   0.462962963  324
80   400000   4.62962963   972
160  4000000  46.2962963  2916

The weight increases three times, since two times seems too weak and
four times to strong.
With the last collector you could power four large 3.75m upgraded
antimatter reactors at full power, but would also need to bring at least
3200 tons to 900 km orbit.
If people want to cheat, they can already add antimatter to their save
file.
I hope I didn't break something.