Rewrite Optimizations using Editor

We need to rewrite the following optimizations using the new editor API:

• CCP
• Forkify
• ForkGuardElim
• Predication

We need to get these ported over for to accomplish a couple of things simultaneously:

1. It's an opportunity to rewrite all of these passes. Rewriting other passes, such as GVN, has been a great opportunity to revisit what the pass is doing in general and make it more clean, concise, and effective.
2. We need to get rid of legacy_repair_plan entirely, so that we can rip out the rest of the partitioning code, including repair_plan.
3. Cava is dying in legacy_repair_plan and/or CCP currently, so these are needed to get cava working as well. This subsumes issue #10 (closed), and is related to issue #9 (closed).