Use the environments cache more often

For a faster experience, particularly on the train.

And the caching logic should be hidden - this replaces
`$cachedEnvironments = $this->loadConfig()->environments[$projectId];`
with
`$cachedEnvironments = $this->getEnvironments($project, false);`

Also includes hiding `drush-aliases` for non-Drupal projects.
- [ ] move createDrushAliases() to the Drupal toolstack