Include into XML import format the definition of per references permissions.

Example:

<git>
    <repository>
        <permissions>
          <read>...</read>
          <write>...</write>
          <fine_grained enabled="1" regexp_usage="true">
            <pattern value="dev/.*" type="branch">
                <write>...</write>
                <wplus>...</wplus>
            </pattern>
            <pattern value="dev/.*" type="tag">
                <write>...</write>
                <wplus>...</wplus>
            </pattern>
          </fine_grained>
        </permissions>
    </repository>
</git>

Limitations & behaviour:

• For each pattern, the value attribute is the path without the "refs/heads/" or "refs/tags" prefix. They are distinguised by the type attribute, that can only be set to "branch" or "tag"
• Global regexp usage is taken into account
  • If a regexp is submitted and the platform does not use the regexp, it's ignored and a warning is emitted
  • If a regexp is submitted and the repository does not use the regexp, it's ignored and a warning is emitted
• When "fine-grained" are used, only <read> global permission is taken into account
  • If there are <write> or <wplus> markups, they are ignored and a warning is emitted