Implement proposal 360: Limiting HSDesc size and amplification

• Revise proposal (torspec!411 (merged))
• Implement framework for reporting suspicious hsdir activity (!3070 (merged))
• Take hsdesc maximum lengths from consensus (!3070 (merged))
• Impose limits on cell counts for hsdir circuits. (!3070 (merged))
• Make sure reports don't leak too much (#2012 (closed))