Using new "Security.login_url" configuration value
Reduced code duplication in ErrorPage (no functional changes)
Merge remote-tracking branch 'origin/3.0' into 3.1
Extracted ErrorPage default data to getter

Allows for less verbose overloading, while still keeping i18n capabilities
in place, which isn't possible with DataObject::$default_records
Excluded Postgres from Travis (breaks build due to internal errors)

We'll need to fix the "no space left on device" issue,
most likely caused by Postgres keeping too much of a query log,
or somehow creating a history of past data.
For now, having a Postgres build breaking the whole
build process (incl. MySQL builds) does more harm than good.
Merge remote-tracking branch 'origin/3.0' into 3.1
Merge remote-tracking branch 'upstream/3.1' into nc0.1