Support for data (dzn) files

[rtaupe]

It shall be possible to specify values for non-instantiated constants in separate dzn files and pass them to the solver via an Executor.

[rtaupe]

On a related note, the diagnosis component currently also does not support models including parameters without values.

For example, if the model includes the statement par bool: somepar;, JMiniZinc will fail with the following exception:

java.lang.NullPointerException: Cannot invoke "String.equals(Object)" because "str" is null
	at at.siemens.ct.jmz.mznparser.MiniZincElementFactory.isBoolean(MiniZincElementFactory.java:156)
	at at.siemens.ct.jmz.mznparser.MiniZincElementFactory.getElementFromLine(MiniZincElementFactory.java:89)
	at at.siemens.ct.jmz.mznparser.MiniZincCP.parseMZN(MiniZincCP.java:51)
	at at.siemens.ct.jmz.mznparser.MiniZincCP.<init>(MiniZincCP.java:34)
	at at.siemens.ct.jmz.ui.VariableDialog.<init>(VariableDialog.java:62)
	at at.siemens.ct.jmz.ui.VariableDialog.main(VariableDialog.java:99)