Tiny new features, more robust localization

What changed:

UI Localization now goes through Localizable strings. This is to avoid having to propagate changes on Base UI to all languages manually, since the UI is simple enough to not have to make language-specific UI choices
Added an option to show battery percentage instead of "Calculating..." when the remaining time is yet-to-be-determined.
Split option to show remaining time in two separate options depending on wether the computer is on battery or on AC power
Began making the notification system more customisable: all percentages are available
Stop depending on Carthage (LaunchAtLogin is deprecating its Carthage support, and Xcode handles dependencies well)

Please let me know if there are things that should be reviewed further

raphaelhanneken / apple-juice