Issues/1792 support for uploading videos

#1792 
Added supported for uploading videos with the following caveats:

- Because the REST API still doesn't support the upload of Videos, I made the app force the use of the XML-RPC api when uploading videos

- Every time when I enter the post view I check if video press is available on the blog. This check should move to a place where blog info is sync from the server.

- I think I found a bug on the WPXMLRPCEncoder. When using this on a HTTP with a body in streaming mode. The encoder was deleting the streaming cache file on dealloc before it could be used on the actual request. For now I just commented out the deletion because these files are stored in the cache folder and will be deleted by the system when space is needed.
The `videoPressEnabled` property on the `Blog` object should be cannonical. Why also track the value as a property on this class vs just checking the blog object?