Add support for move operation

This implements non-recursive move for S3 and WebDAV.
There are a few different error codes, listed here: http://msdn.microsoft.com/en-us/library/aa142926(v=exchg.65).aspx

However, mapping them to the correct FSP error codes is larger project (#21). I wanted to have a discussion with @mtomasz-chromium about that, because I don't know the details of what his error codes mean, and it may be the case that new FSP codes are needed.

Whatever happens, it should be handled in the low-level WebDAV client to avoid duplicated logic between event handlers. I can change this to the generic 'FAILED' in the meantime and we can start a discussion about how to set up useful error reporting?