Related to https://github.com/mattermost/platform/issues/643
Also request from @botherder: https://twitter.com/botherder/status/655394442313138176
Forum issue: https://forum.mattermost.org/t/how-do-i-set-the-base-url-for-apache-ssl-forwarding/573
To achieve this change, the client should reference the Site URL config.json setting instead of a relative link, when one is available. If no site URL is set, then return a slash or a blank value.
1) For someone to host Mattermost in a subdirectory, it is assumed that Site URL is required to be set.
2) This change should not break existing deployments, including those who don't have Site URL set.
3) Preliminary work from in 2016 can be found here: https://github.com/mattermost/mattermost-server/compare/master...akihikodaki:PLT-200