Default policies

[ammen99]

This also contains #56 since they will be needed for implementation of the policies (and the unit tests for them are disabled since they are failing)

• [x] DefaultCostFunction

• [x] DefaultNonPreemptiveDistributionPolicy

• [x] DefaultBlockingDistributionPolicy

• [x] DefaultPreemptiveDistributionPolicy

• [x] Take swap space into consideration (needs some more though)

EDIT: fixes #78

[ammen99]

LGTM, needs rebase, my IDE notifies my that in some places you are dividing float - int and assigning it to int, but if flake and mypy don't mark it as a problem.

Which lines?