IA: more tutorial links
IA: Tutorials stuff
- Move 'Cancel or Skip a Transaction' to 'About Canceling a Transaction'
(Fixes#582)
- Add more 'See Also' links to Escrow & Payment Channel tutorials
- Split ledger history section into a parent concept page w/ online
deletion and history sharding as child pages
- Clarified how much data is stored in general
- Covered the special case for backfilling with advisory_delete enabled
(including updating the diagram)
- Changed full history recommendation to NuDB only