title: Plug into the hierarchy of Spring Boot property sources
body: <p>I know the default order of spring's properties sources: <a href="http://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html" rel="nofollow">http://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html</a>
  how can i add my own property source with a specific precedence?</p>
  
  <p><code>@PropertySource</code> is not enough as it adds new properties with very low priority</p>