Precache some of the urls

[mdeora]

Currently there is no provision to precache some urls before they are used.

[arvkmr]

In addition it would be nice if we can precache only specific range of the media. For example precaching a Mb for a file that is 20mb in length so we can start playback with AVplayer instantly when we play the file..

[libobjc]

Use this API to precache.

/**
 *  Create the data loader for the request.
 *
 *  @param request : The request of the expected data.
 *  @return The data loader for request.
 */
+ (KTVHCDataLoader *)cacheLoaderWithRequest:(KTVHCDataRequest *)request;