ZODB Components: Before migrating Interfaces from FS, there must be one Interface class per source file matching its name.

Same as Document class: this avoids registering Interfaces at startup and just do it
when using the Interface. In assuming that portal_components/XXX has a class
name equals to XXX.getRference(), it is easier to:
 * List all existing Interfaces (for example in Portal Type Class view): getReference()
   on all validated 'Interface Component' in portal_components.
 * Lookup for an 'Interface Component': 'from erp5.component.interfaces.XXX import XXX'.