#295 XmlValidator normalizes line endings when checking formatting

Note that this change means that `XmlValidator` will only check for formatting while ignoring line endings, since it converts everything to Unix-style internally. Thus, it won't matter what the line endings of the actual XML are or which platform you're running Qulice on.

For the line ending checks, we have Checkstyle, so I think it would be redundant to check for that in `XmlValidator`.