Correction factor plots should not be generated in all cases

[Nicklas Nordborg]

Currently, correction factor plots can be created for all 2-channel bioassay sets that have a parent bioassay set.

But if the child and parent bioassay set are in different data cubes the reporter/position mapping may differ which means that the correction factor plot either fails (with a NullPointerException) or the generated plot compare spots with different reporters.

The background is that the correction factor plot only uses the position coordinate to match spots between the parent and child bioassay set. As long as the parent and child are in the same datacube a given position always maps to the same reporter, but in different datacubes the mapping can be different. If child bioassay set have position coordinate not found in the parent bioassay set the result is a NullPointerException:

java.lang.NullPointerException
  at net.sf.basedb.util.plot.ScatterPlot.addData(ScatterPlot.java:106)
  at net.sf.basedb.clients.web.servlet.PlotServlet.generateCFPlot(PlotServlet.java:735)
  at net.sf.basedb.clients.web.servlet.PlotServlet.doGet(PlotServlet.java:401)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)

[Nicklas Nordborg]

(In [6301]) Fixes #1765: Correction factor plots should not be generated in all cases