Added Global Setting to Server config tab to
  - Enable & Disable the feature
  - Set the Proxy HTTP & HTTPS Ports

Added Per site level switch to enable and disable feature (Located in the Web Tab under the advanced section)

Added Apache2 and Nginx vhost updates to enable proxy_protocol on the listen lines

Added New database column to web_domain called "proxy_protocol" to enable site level config (Patch file Added upd_0089.sql)

Updated the Base Table SQL file to include "proxy_protocol" field

Patch misc

See merge request !920

show ips only with vhost = y and  show directive_snippets for the admin even...

See merge request ispconfig/ispconfig3!929

show ips only with vhost = y and  show directive_snippets for the admin even if they are set to customer_viewable = 'n'

- added possibility to execute mkdirpath, file_put_contents and file_get_contents as unprivileged user, partly implements #5417

Dutch translation

See merge request !921

Helmo authored Sep 24, 2019 and Till Brehm committed Sep 24, 2019

Some form of inheritance might be nice to reduce the amount of duplication in these files.

Check explicitly for session username, fixes #5389

See merge request !922

Added option to select Local Mail server for remote email accounts import

See merge request !924

- ignore @/*@ targets for spamfilter_user in rspamd plugin