Contractor Combining

This PR is the first step in eliminating the price gouging issue that we're seeing with our hosts. I've tried to keep things functionally equivalent at this point to how they used to run, which means that we haven't solved all that many problems.

But, instead of having 3 separate loops responsible for creating contracts, I've moved them into a single loop that handles everything.

Creating an allowance is no longer a blocking call. This broke a lot of tests, but I have since fixed them. There may be an NDF or two lying around still.

This is the first stage, and should be merged on its own to prevent this PR from blowing up the way my last PR did. The next step will be to add a IsGoodForUpload and IsGoodForRenew field to the RenterContract, which will allow us to disable hosts that are evil.

That should do it for v1.3.0. There's still a lot more things we should be doing with the allowance management, but it'll have to wait until v1.3.1