Changes:

- switch to simple majority of >= 505/1008 blocks
- add REQ-MINFEE-ACTIVATION-ANCHOR
  (to set starting fee to 1000 sat/kB when the CHIP first calculates)
- add risk of miners rejecting the responsibility to manage relay fees
- add risk of excessive fee rate granularity
- add risk of reduced fee rate stability
- update the projected fee table to use 500 sat/kB for typical txns
- rename REQ-MINFEE-ACTIVATION to REQ-MINFEE-ACTIVATION-FLUSH
- spell check fixes
- update references, acknowledgments, timelines