Various improvements, mostly having to do with large files.

[dworkin]

• Upgrade integrated WebDAV client from Itay Sagui to 1.1.4, to get partial up/download functionality.
• Include explicit GPLv3 license file.
• Fix some minor path-handling bugs.
• Use chunked mode to upload files.
• Disable 4G limit check to allow up/download of large files.
• Use streaming upload when FlushMode == FlushAtWrite.
• Use byte ranges for read requests (don't download and cache the entire file).

[FrKaram]

Thanks for the huge contribution. I'll have a look at it ASAP