Spring Boot: use hierarchy of the contexts

[php-coder]

During migration to Spring Boot we switched back to using a single context.

Example:

- SpringApplication.run(ApplicationBootstrap.class, args);
+ new SpringApplicationBuilder()
+ .parent(ApplicationContext.class)
+ .child(DispatcherServletContext.class, H2Config.class, ErrorPagesServletContainerCustomizer.class)
+ .run(args);

See also: http://docs.spring.io/spring-boot/docs/1.3.3.RELEASE/reference/htmlsingle/#boot-features-fluent-builder-api

Tech debt for: #75

[php-coder]

Might be helpful:

• https://ccbill.com/blog/spring-boot-and-context-handling
• https://dev.to/__nikolamicic21/multiple-hierarchical-contexts-in-spring-boot-25nf