Restrict usable characters for "silecs-device-label"

Fixes #97

silecs-model/src/xml/DeploySchema.xsd

@@ -607,8 +607,8 @@
     <xs:simpleType name="DeviceNameType">
         <xs:restriction base="NonIdentifierType">
             <xs:minLength value="1" />
-            <xs:maxLength value="30" />
-            <!-- In FESA the deviceName is restricted to max. 30 characters -->
+            <xs:maxLength value="30" /> <!-- In FESA the deviceName is restricted to max. 30 characters -->
+            <xs:pattern value="[_A-Za-z]+[_A-Za-z0-9]*"/> <!-- Needs to fulfill plc-specific language standards -->
         </xs:restriction>
     </xs:simpleType>