changelog: prevent from 500 errors on changelog when fetching certain commits.

commits: add protection against 500 errors on commit children/parents page.

login: don't use request.params because it allows to passing multiple values for GET which can confuse the system.

repo-summary: protect against wrong commits in repo summary.

i18n: fix typo

docs: added gzip into static files for nginx

docs: added 502 page instructions for nginx and apache

commits: hide evolve commits. Fixes #5392

user-groups: fix potential problem with group sync of external plugins. - when using external plugin we used to check for a parameter that set the sync mode. The problem is we only checked if the flag was there. So toggling sync on and off set the value and then left the key still set but with None. This confused the sync and thought the group should be synced !

auth: add more login when performing sync of user groups.