VLCDownloadController: Improvement of progress percentage and time remaining along with some addition.

In this merge request, VLCDownloadController has been improved. The improvement are as follows - earlier users were not able to see the progress of the file that they were downloading if vlc was not able to fetch the file size before hand or it was unknown, after this change, vlc will be able to know the file size before hand, i.e. before downloading the file itself and hence provide users with correct progress of their download, i.e Percentage downloaded and time remaining.

Along with these, a new feature has been added, from now on, an announcement will be made at the completion of the download.