Added support for only downloading main file and optional subs

Added support to Transmission for options:

main_file_only: (true|false)
include_subs: (true|false)

If set to true, main_file_only will only select a file that's 90% of the size of the torrent or larger for download.
If set to false, main_file_only will not modify files set to download at all.

If set to true, include_subs will also set sub files (*.sub, *.idx, *.srt) to download in addition to the main file.
If set to false, include_subs will do nothing.
If main_file_only is set to false, include_subs has no impact on the downloads.

In addition, the "addpaused" setting was changed to not set when adding the torrent, this allows the script time to grab the added torrent, process the file list for the above values and then set the torrent to start if "addpaused" was set to "no." This prevents the client from starting downloads on files in the torrent the user doesn't actually want.
PEP8 incompatible variable name