Save emote list on a per subreddit basis to allow the app to only
load the emote list of subreddits that are going to get synced.

Emote lists are now only updated if new emotes are added, allowing
the app to abort the download and parsing of the list if nothing
has changed.
Check if file exists befor trying to open it
Merge remote-tracking branch 'upstream/master' into emotes_per_subreddit
Merge pull request #21 from Trellmor/emotes_per_subreddit

Emotes per subreddit