Allow overriding of versioning rules from XML extensions

Since NXS-528, all document types are given a default versioning policy (waiting for it to be configurable in the interface), but this is added after XML extensions contributions, so it's not possible to customize them in the mean time.

Steps to reproduce:

• create a document type "MyDoc" and give it the "Versionable" facet => it will have default version increment
• add an xml extension with following configuration:

<extension target="org.nuxeo.ecm.core.versioning.VersioningService" point="versioningRules">
  <versioningRule typeName="MyDoc">
    <initialState major="0" minor="0"/>
    <options lifeCycleState="*">
      <!--<none default="true"/>-->
      <minor default="true" />
      <major/>
    </options>
  </versioningRule>
</extension>

=> the custom configuration is not taken into account