BioAssaySetExporter should attach generated files to the bioassayset

[Nicklas Nordborg]

The main reason is that we want to change the MeV launcher so that it requires a pre-generated MeV file instead of doing a new export every time. This should considerably increase performance since the MeV file generation usually takes a lot of time. See ​http://baseplugins.thep.lu.se/ticket/162

What we need to do:

• Define a some new data file types: MeV, Serial BASEFile, Matrix BASE file.
• Implement a DataFileValidator and DataFileMetadataReader for BASEFile:s
• Add code in the BioAssaySetExporter that attaches exported files to the bioassay set. This should be an option that default to true. If an older file is already attached the plug-in might also ask if the existing file should be deleted (from the BASE file system) or not.