Create a note for every imported commit containing svn metadata

Create a note for every imported commit containing svn metadata

To provide metadata from svn dumps for further processing, e.g.
branch detection, attach a note to each imported commit that stores
additional information.  The notes are currently hard-coded in
refs/notes/svn/revs.  Currently the following lines from the svn dump
are directly accumulated in the note. This can be refined as needed.

 - "Revision-number"
 - "Node-path"
 - "Node-kind"
 - "Node-action"
 - "Node-copyfrom-path"
 - "Node-copyfrom-rev"

Signed-off-by: Florian Achleitner <redacted>
Acked-by: David Michael Barr <redacted>
Signed-off-by: Junio C Hamano <redacted>