Set plug-in to Java 7
Add isValid to NullFunction to fit additive API change

See scisoft-core.git
commit 4aa3eb6382eaf1cb80d3e1336e25046012569cf3
Author: Tracy Miranda <github@tracymiranda.com>
Date:   Mon Feb 24 18:30:28 2014 +0000

    Add isValid() to IFunction and implementations

    This is used by FunctionFittingTool to determine correctness of the
    function tree. Also for functions which can be incorrectly configured
    like JexlExpressionFunction it is quite valuable
Function Fitting Tool Implementation
Merge branch 'function_fitting'
Merge remote-tracking branch 'origin/master'