convert_legacyEmuDB_to_emuDB() should check duplicate label entries in .tpl

[raphywink]

Just had the case of following bad entries in a legacyEmuDB .tpl file:

! label types at each level
label Word Word
label Phonemes Phonemes
label Targets Targets

The conversion works but produces a broken DBconfigJSON:

...
  {
      "name": "Targets",
      "type": "EVENT",
      "attributeDefinitions": [
        {
          "name": "Targets",
          "type": "STRING",
          "labelGroups": [
            {
              "name": "are",
              "values": [
                "first",
                "second"
              ]
            }
          ]
        },
        {
          "name": "Targets", <- SIC! duplicate attributeDefinitions$name entry
          "type": "STRING"
        }
      ]
    }
...

convert_legacyEmuDB_to_emuDB() should probably throw an error if it encounters these bad entries.