Added wildcard and property placeholder support

... in the SpringApplication String defined sources

* Default resource loaded in the BeanDefinitionLoader has
been changed to PathMatchingResourcePatternResolver;
* A check for the ResourcePatternLoader similar to that in
AbstractBeanDefinitionReader and property placeholder
resolution has been added to the load(CharSequence) method
of the BeanDefinitionLoader;
* Added a unit test illustrating the issue;