disable "server_status": "/debug/status" by default and explain its use

zh-TW templates, improve language matching, add issing languages to c…

…onfig

bug fix in optionalHttpHeaders; deprecated ioutil removed

add HTTP headers: X-Frame-Options, Referrer-Policy

Merge branch 'devel'

fixing comments

instructions on creating a private installation

postgress: reduce the number of open connectins to fit under default …

…limit

adding ukrainian translations

Merge pull request #878 from tinode/session-sub-race-dev

Fix a race condition around Session.subs.