Update config / code styles for 4.0

[tractorcow]

Related https://github.com/silverstripe/silverstripe-framework/issues/7590

Fixes include:

• support for getenv for _configure_database.php
• coding style enhancements
• update CI config to trusty

[tractorcow]

Build is broken but it's still better than the prior breaking build. :)

[tractorcow]

I've updated as much as I can... there are other issues but are pre-existing, or in framework regressions.

[tractorcow]

Ok, updated @dhensby