migrate: Bugfix arguments.join()

arguments is not an array, so it does not have a join() method
Merge pull request #1285 from mc10/migrate

migrate: Bugfix arguments.join()
nightMode: Create separate night mode module
nightMode: Add night mode file to browsers
styleTweaks: Minor copyedit to option
nightMode: Begin migrating from styleTweaks to nightMode
migrate: Migrate nightMode settings
nightMode: Rename useSubredditStyleInDarkMode

Description slightly altered as well to reflect the change.
nightMode: Improve description of lightSwitch
styleTweaks: Use === instead of ==
migrate: Add moveStorage function for moving RESStorage options
migrate: Add moveStorageWithFunction function
nightMode: Migrate RESmodules.styleTweaks.nightModeWhitelist
styleTweaks: Fix spacing
styleTweaks: Slightly adjust use of jQuery variable
styleTweaks: Replace `this` with modules['nightMode']