Expand into "anonymous download" : upload+rename

Which part would be affected

The remote.inc utility lib's method linked to remote.transfer()

Description of the feature

1. Allow to provide a different name for the file, the "random name" feature from anonymous mode being a sub-case rather than its own feature like it is currently
2. Make sure that uploads are also able to rename the file on the server-side (to avoid cloggering logs from the client)

How would it enhance the experience?

Auto-renaming a file when uploading would allow, for example, to upload a lib from a breached system into a versioned file name
It's therefore an important building block for #27

Checks to do

1. Non-renamed transfer must be possible
2. Anonymous downloads should still be possible, however :
   2a) No script use the feature yet, so backward-compatibility is not a concern
   2b) Said feature is currently unavailable due to a critical Greyhack bug ( issue #32 , GH bug 398 ), making impossible to reasonably test/use it