finally I saw the light, MediaAria2 now inherits MediaCurl, therefore

finally I saw the light, MediaAria2 now inherits MediaCurl, therefore
has access to curl methods, or any functionality which aria does not provides.

Implemented the following options with aria:

download.max_concurrent_connections (default 2)
download.min_download_speed (default no limit)
download.max_download_speed (default no limit)
download.max_silent_tries (default 5)

Lot of duplicated code removed, and no longer require command line curl.

Now lets see if we can remove duplicated code in curl iteself and also
implement range support.