Project archive need to use subfolders per site

[Nicklas Nordborg]

The main reason is that we need to be able to split the data onto multiple disks which will be easier if we can create symbolic links per site.

This should not be too complicated to implement for new items. In some parts this is similar to what has already been done for external items (see #785), but we don't need any extra configuration settings.

Ideally, existing items/files should be moved to the new structure. This will need careful planning so that everything in BASE that directly or indirectly references the files are updated.

[Nicklas Nordborg]

(In [4551]) Fixes #981: Project archive need to use subfolders per site

This should be implemented for new items now. The changes MergedSequences.generateDataFilesFolderForProjectArchive() should be enough for this to propagate to all downstream places.

The Reggie.convertDataFilesFolderToBaseFolder() still need to handle the old case when converting the path to a BASE file system path.

Existing items/files will remain at the existing location, but it is possible to move them.

1. Move the files in the project archive.
2. Update the DataFilesFolder annotation on all DerivedBioassay and RawBioassay items. It should be easy to fix with a batch export/import.
3. Update the URL property for all file items that are referencing files in the project archive. Use the "Search" function to find all files and then the batch export/import to update. Use the ID property for references.