Q4 2017 Refactor

• Polymer 1.x/2.x hybrid support
• range property no longer exists, use fromMoment and toMoment as the source of truth - fixes the problem of flickering / multiple event calls when any of the three properties were changed in the past
• Rangepicker will now have an empty state if fromMoment and toMoment are not specified or picked by the user (#32)
• Now uses iron-dropdown for more intelligent positioning of the range panel dropdown (#18)
• Updated min and max to minDate and maxDate to align with field
• Added fromMoment and toMoment arguments to validate function call
• Updated tests