Move actionbutton into Shiny proper
Add date picker widget
Remove unused helper file
updateDatePickerInput: make sure value is a string
Add date range picker
Rename datePickerInput to dateInput, and dateRangePickerInput to dateRangeInput
Remove unneeded clientData argument from update inputs
Convert dates to Date objects on server side
Switch to eternicode version of datepicker
dateInput: add support for custom date formats
Use correct jQuery wrapper for fileInputBinding.find()
Add initialize() method for input bindings
Datepicker: use yyyy-mm-dd as canonical format

Other formats, like mm/dd/yy, are simply used for display.
The initial value is set with the tag 'data-initial-date', instead of 'value'.