Cleaned mail viewing scripts

1. fix api calling. 2. move mail viewing functions to bbs_mail.js 3.
wrapping ansi2html function. 4. adding corresponding constants to
config.js 5. removing duplicate bbs_post_info declaration.
Cleaned mail ui codes

1. re-fixing path term bug on no responding. 2. removed or commented all
functions on writing mails. 3. consistent ui for mail content viewing
and post content viewing. 4. adding comments.