Handle resolution per show

[mtshrmn]

Apparently, new shows don't always have 1080p resolution. A neat feature is to allow each show to overwrite the specified resolution.

Suggestion:

[settings]
resolution = 1080
download_dir = ~/Videos

[subscriptions]
show1 = 19
show2 = 04
show3 = 07

[resolutions]
show2 = 720 ; overwrites the resolution specified in the settings section

and when subscribing to a show: $ horrible-downloader --subscribe "show2" -r 720