Improve performance by not scanning ignored files

I ran into some performance issues with GitKraken on slower (HDD) storage. When debugging I checked which files GitKraken was accessing and a lot of access was in ignored files (like node_modules). Sometimes GitKraken would show all ignored files as changed in the UI, only to correct itself later when it realizes those are ignored files.

It would be a great performance improvement if it wouldn't scan ignored files to begin with. Not a big issue on modern high IOPS SSD drives, but when working with a older, slower machine with a slow HDD, this would really help a lot.