apply constraints to names for tasks and task instances in resource configuration

The same rules as for IEC identifiers are applied.
- no non-lating characters, ...
- no IEC keywords
- check for duplicate names in resource configuration

closes #19

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                  <xsd:element name="Linux">

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                    <xsd:complexType>

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                      %(toolchain_gcc)s

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                    </xsd:complexType>

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                  </xsd:element>