Coordinator improvements

About heaviest branch selection, I think attempting to look for the heaviest branch is overrated. This idea assumed that different users will more or less have similar hash power but we know that in reality this is not the case.

Now that “white-flag” solution is on the table, I am thinking we should go about even easier solutions. While speaking to @darcy.camargo, he claimed that with “white-flag” URTS can be fine. Not sure that I fully agreed/understood but currently I am in the opinion that we should do the following:

When looking for transactions to approve without promotion: (almost) URTS on a subset. This may mimick some LM properties I think. It will help the tangle grow in a steady direction if I understood correctly. Since we’re using “white-flag” the drawbacks of it are minimal.

When doing promotions (for coordinator checkpoints we need this):
Perform at least one LM weighted walk to get a tip. For the other tip you can do maybe URTS, or almost URTS to approve left behinds.