Adds a JGit built-in implementation of the "git lfs smudge" filter. This
filter should do the same as the one described in [1] besides that it
only supports the local case when the lfs objects are already present in
the media directory. Remote cases where download of LFS objects from an
LFS server is needed will be done in a later commit.
[1] https://github.com/github/git-lfs/blob/master/docs/man/git-lfs-smudge.1.ronn
Change-Id: I8ff661d4edd3667ef7f86f3b4fa33e568eb4c8f4