#592 Unify cif2plc and plcgen model classes

• Added PlcTarget to the writers for access to the model text generator.
• Removed PlcValue class.
• Renamed OutputTypeWriter to Writer class.

The other copied classes seem fine for now (see #592 (closed) for a list). Likely the target-specific writers need more work eventually but that seems a bit premature for now.

Addresses #592 (closed)

Note: "Organize imports" made the following change:

index 74a08bd98..59dcc73c9 100644
--- a/cif/org.eclipse.escet.cif.plcgen/src/org/eclipse/escet/cif/plcgen/model/functions/PlcSemanticFuncDescription.java
+++ b/cif/org.eclipse.escet.cif.plcgen/src/org/eclipse/escet/cif/plcgen/model/functions/PlcSemanticFuncDescription.java
@@ -13,8 +13,6 @@
 
 package org.eclipse.escet.cif.plcgen.model.functions;
 
-import org.eclipse.escet.cif.plcgen.model.functions.PlcBasicFuncDescription.ExprBinding;
-
 /** Function description extended with the semantic operation being performed in a function application. */
 public class PlcSemanticFuncDescription extends PlcBasicFuncDescription {
     /** The semantic operation performed by the function application. */

It's needed to avoid a warning in JavaDoc, but it's apparently thus not recognized in for that in the JDT.