code review

- Code was not formatted
- Seems to be inconsistencies between 5.9.5 and 5.9.6-SNAPSHOT versions in dependencyManagement, parent POMs...
- Removed useless/conflicting imports
- Moved version definition to dependencyManagement, out of dependencies.
- Removed custom Maven repository (bad practice preventing the provisioning of our Nexus caches)
- Removed weird comments
- Updated remaining deprecated configuration about nuxeo-imagemetadata-utils-demo*
- Didn't fix the broken test org.nuxeo.imagemetadata.test.ImageMetadataReaderTest
- There are much more third-party dependencies in the generated MP
  - not sure which packaging method you wanted to use (recommended, nonxr or explicit)
  - if you want less, then either
    - use a nx:zipdiff like in the recommended method
    - reduce the scope of what goes in install/lib (i.e. explicit includes instead of negative includes)
    - wait for the artifact:nuxeo-expand depth being implemented  
        `<artifact:nuxeo-expand includeTestScope="false" groupPrefixes="org.nuxeo.imagemetadata" depth="1" />`

- Removed deprecated use of copy command in install.xml  
=> use the update command
- Add compliance with 5.9.5 (for testing purpose?) but aligned on 5.9.6-SNASPHOT (see above remark about versions inconsistencies)