Added customSubtitles plugin
Custom Subtitles

Added customSubtitles plugin initialization.

· Huge cleanup on CustomTrackMenuItem.prototype.loadSubtitle's hack:
Downloading, Decompressing, Decoding process was split on separate
functions. (getSub, decompress and decode)
· getSub also supports local file system subtitles.
· decompressing is only done when the file extension is .zip
Merge branch 'master' of https://github.com/popcorn-time/popcorn-app into feature/#19
Merge branch 'feature/#19' of git://github.com/ivantodorovich/popcorn-app
Adds support for custom subtitles.