Extract methods for source and target document upload.

    This is a preliminary step in moving this code into separate classes.
make FileService.isNewDocument static (mikado method)
make FileService.sourceUploadSuccessResponse static (mikado method)
make FileService.getInputStream static (mikado method)
make FileService.combineToTempFile static (mikado method)
make FileService.combineToTempFileAndDeleteUploadRecord static (mikado method)
make FileService.persistTempFileFromUpload static (mikado method)
make FileService.isDocumentUploadAllowed and .checkValidSourceUploadType static (mikado method)
make FileService.checkSourceUploadAllowed static (mikado method)
make FileService.retrieveUploadObject static (mikado method)
make FileService.checkUploadPreconditions static (mikado method)
make FileService.checkSourceUploadPreconditions static (mikado method)
make FileService.saveUploadPart static (mikado method)
make FileService.parsePotFile static (mikado method)
make FileService.processAdapterFile static (mikado method)
make FileService.tryUploadSourceFile static (mikado method)
move all source upload methods from FileService to new DocumentUpload (mikado method)
make tryUploadSourceFile an instance method (mikado method)
make helper arguments for source upload into instance fields (mikado method)
make source upload helper methods private (mikado method)