Updates and applies JSHint settings

- Adds all available enforcing options in JSHint rake task.
- Removes unsupported options in JSHint rake task.
- Cleans up JS according to stricter JSHint settings (with 2
exceptions: the regex in the feedback form manager and the many
statements warning in the function in the popup-manager).
- Refactors character limiter code to use event handler function.
- Removes unused code from details map manager code that was leftover
from when the nearby markers were present.