Deprecate the FilesUploader constructor that takes no UploaderService

We really should reuse any existing one. To make things easy for
users, they can pass null in which case we will construct a fresh
UploaderService.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use more appropriate name for FilesUploader#initialUploader

The name 'initialUpload' suggested that it would perform the complete
upload, but it is still the duty of the user to take care of logging
in, uploading and logging out.

While at it, add a signature accepting an uploader service and
deprecate the old call.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fixup! Deprecate the FilesUploader constructor that takes no UploaderService
Use only the new constructor of the FilesUploader

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Avoid using the PluginInfo constructor deprecated in newest scijava-common

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Avoid using the deprecated FilesUploader#initialUpload method

... for the reasons why it was deprecated...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fixup! Add an integration test for the uploader auto-install