Switch to DRYer organization of configurations

Adds an application.common.dev.yml, and 'common' section in YAML files.
Precedence is as follows:

1. Environment-specific config in application.{theme}.dev.yml
2. Common config in application.{theme}.dev.yml
3. Environment-specific config in application.common.dev.yml
2. Common config in application.common.dev.yml
Version bump