Fix bug where the class ConnectionCodeGeneratorTest call fails if run on UNIX/Linux:
- Add '.gitattributes' to always have LF line endings on checkout for the '*.st' template files.
- Reverted the resource 'PartnerConnection.java' used by ConnectionCodeGeneratorTest to validate the rendered Java code by removing the previously added empty lines. Indeed those empty lines were intended to make it work on Windows but then make the test fail on UNIX/Linux).

More details:
- Differences between StringTemplate v3 and v4: "\n in a template becomes \r\n or \n in output depending on platform." (http://www.antlr.org/wiki/display/ST4/Differences+between+v3+and+v4)
- Declare files that will always have LF line endings on checkout. (https://help.github.com/articles/dealing-with-line-endings)