The current file path for decoration will be confusing for developers. Make two changes to improve developer experience, as agreed upon in meeting https://jira.magnolia-cms.com/browse/DEV-188.

For reference, the current path as implemented (and to be changed) is:
/extensions/<definition-type>/<destination-module>/<definition-path>/<file-name>

Todo:
1. Change "extensions" to "decorations".
2. Swap place of <destination-module> and <definition-type> in the path.
So the final path should be:
/decorations/<destination-module>/<definition-type>/<definition-path>/<file-name>