add --strategy to choose the strategy to use

`--strategy random` or `--strategy binpacking:<overcommit>`

default: `--strategy binpacking:0.05`
I agree that's not optimal, but I'm delaying the decision until we have a strategy with more options :)

If we get alot I was thinking about a JSON config file, and for the lazys: `--strategy "binpacking:{OvercommitRatio:0.05}" `