webv4: consider translating UTF-8 before posting message

Most BBS software and clients, including Mystic, don't understand UTF-8. So when some systems post messages with the web client, their use of single right quote is indecipherable for people. Synchronet and SyncTERM do not have a problem posting/displaying.

I know at least iOS and iPad OS have the posting issue.

https://www.fileformat.info/info/unicode/char/2019/index.htm