RFR: 2163: Add API to Repository for working "git notes" [v2]

[Erik Duveblad]

> Hi all,
> 
> please review this patch that adds the methods `addNote`. `notes` and `pushNotes` to `Repository.java` to allow Skara code to work with [git notes](https://git-scm.com/docs/git-notes). This will be used in another patch to implement a "git note"-notifier (see https://bugs.openjdk.org/browse/SKARA-2164). 
> 
> I opted for a fairly minimal API here even though the `git notes` command exposes many more features. I also decided to add the `pushNotes` method although callers could use the `push(String refspec, URI uri)` variant because I don't like the notes refspec to "leak" out into other parts of the code.
> 
> Also added a couple of unit tests.
> 
> Thanks,
> Erik

Erik Duveblad has updated the pull request incrementally with one additional commit since the last revision:

  note -> lines

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1607/files
  - new: https://git.openjdk.org/skara/pull/1607/files/b6aabbda..214ff2b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1607&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1607&range=00-01

  Stats: 6 lines in 3 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/skara/pull/1607.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1607/head:pull/1607

PR: https://git.openjdk.org/skara/pull/1607