JGit 3.7 New and Noteworthy

# JGit

## Features

- Add basic support for .gitattributes
- Use slf4j for logging
- Introduce hook support into the FS implementations (on Posix and Cygwin)
- Support for the pre-commit hook
- Provide more details in exceptions thrown when packfile is invalid

## JGit Command Line

- JGit command line: add option --orphan for checkout command

## Build and Release Engineering

- Update build to use Tycho 0.22
- Use target platform DSL and generator to maintain target platforms