ux: fix show inline comments link

ux: add comments id to comments form so that linking to comments works

pullrequest: remove old diff code from pullrequest controller

system-info: indicate http mode is default when not set inside config.

docs: introduced new docs section upgrade notes. It will store important information about upgrading.

vcs: raise better exception if file node history cannot be extracted. reference: #4664

pull-requests: also expose universal url as singular form.

diffs: fixed other file source when using pull requests. It must use other repo for fetching proper commits.

diffs: added wide-mode button to expand large diffs.

pull-requests: added version browsing for pull requests. - invalidated comments now link to previous version to show code context - removed all deprecated JS code left from new diffs - improved invalidated comments display logic - UI tweaks