A few improvements

Hi @willmorgan, here are a few improvements I've made.

Sorry they are all bunched up - I consider them fairly minor, and they are all backwards compatible.

Happy to split up into separate pull requests, if needed.
`silverstripe/framework` requires `composer/installers` ...I've only just realised this.
Do you think that we can then safely assume this requirement for all modules? I've never specifically required it.