General improvements

I hope you appreciate these improvements:

* Added proper .gitignore.
* Remove class methods initWithDelegate: (used instance ones).
* Remove initWithDelegate: methods from subclasses of BRRequest (just BRRequest has the initWithDelegate: method).
* Code conventions.
* Fixed shouldOverwriteFileWithRequest: method never called (https://github.com/lloydsargent/BlackRaccoon/issues/12).
* Fixed warnings.
* Added fullRemotePath to BRRequestDownload and BRRequestUpload.
* Added uuid property to BRRequest.
* Added passive mode (by @colinhumber).