Reservation notes should edit in Append mode

[dgoerger]

Currently a qualified person can edit a reservation and delete all past notes. We should switch the box from Edit to Append, so no history gets lost or maliciously deleted. If an admin wants to redact a previous note, they can just leave a note indicating that the previous was in error.

[dgoerger]

We might also consider adding e.g.

===FILING NOTES===
The following was added to the logfile for this reservation when the reservation was first created, on [long timestamp].
[ note text ]

for each appending step, with timestamps.

[orenyk]

This was completed with #872, closing!