Clarify rules and docs related to PV type/classification

[Hans5958]

• Remove definitions of types from "Correct PV type" rule to link the respective PV type/classification rule page instead to reduce duplication
• Shorten excerpt and explain further for each type rule page (too short? read the page!)
• Put related rules (from the Song entry editing page) into each PV type/classification and related rules
• Move "Region-blocked" rule embed to "Original PV deletion" rule page to reduce confusion

I was going to remove the PV type in favor of just linking the "correct PV type" rule, but then I just leave it there for now.