*Title: Template listing for datatypes

Incentive:
Let the datatypes return which templates they depend on.
This list of templates will be used by the export system
to pick related templates more correctly.

*Documentation:
Add a new method templateList() to eZDataType. This will return
an array with template files to search for either as a filepath
or as a regular expression.
A return value of false means no template relations.

Datatypes that has this implemented:
eZXMLType - Provides ezxmltags relation.

*Testing:

*SVN Revisions: