[ResourceBundle]  added the ability to configure services, forms, twig extensions, validations and mapping using yml or xml files (or both)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | #2091
| License       | MIT
| Doc PR        | #2091

I don't know why this bundle uses XML files for configuration and mapping, but personally i like more work with YAML files, is more simple for me.

With this changes, if someone want to configure the mapping of a bundle using YAML files, only have to change the mappingFormat variable value to 'yml' on the bundle class. To use YAML for the configuration files (services, form, twig, etc) only have to change the configFormat variable value to 'yml' on the bundle extension.

Also mixed scenarios are possible (mapping in XML and config/services files in YAML or viceversa).
@stloyd you're right!