validate eln annotations

@constraint
def unique_names(self):
    names: Set[str] = set()
    for base in self.extending_sections:
        for quantity in base.quantities + base.sub_sections:
            for alias in quantity.aliases:
                names.add(alias)
            names.add(quantity.name)

    for def_list in [self.quantities, self.sub_sections]:
        for definition in def_list:
            assert definition.name not in names, 'All names in a section must be unique. ' \
                'Name %s of %s in %s already exists in %s.' % (definition.name, definition, definition.m_parent, self)
            names.add(definition.name)
            for alias in definition.aliases:
                assert alias not in names, 'All names (incl. aliases) in a section must be unique. ' \
                    'Alias %s of %s in %s already exists in %s.' % (alias, definition, definition.m_parent, self)
                names.add(alias)