Fix random seed and add 'seed' as parameter

[jdevost]

Description

I noticed the Random function wasn't working: It was random, but always in the same order.

We don't need to pass a Random object around, we simply need to set rand.Seed() once. Then all call to math/rand will be randomize.

It can be useful to set the seed directly to run the bot in a predictable fashion (ie. unit tests), so I added support for a -seed parameter.

[erocheleau]

Did you test it? :D

[jdevost]

Yes, I tested the -seed. It works as advertised.