Drop LDAP support.

See #3337
Sync some styles with core
Drop remnant of LDAP support
Docs cleanups
Upgrade: Direct upgrade from pre 2.6.0 is no longer available

Followup for 48031542.
Upgrade: Drop the upgrade machinery for pre 2.6.0

This can be safely dropped since we no longer support direct upgrades
from versions older than 2.6.0.

Also cleanups on initdb, docs and Fabric script.
Templates: implemented generic about page

Brings back stock Pootle content.

Fixes evernote/pootle#262.