Time support plugin

WIP :construction: 

This PR:

* adds the ability to register plugins with the date range picker - using the same basic plugin architecture from the Tabler codebase.
* adds a time support plugin which when enabled renders a panel within the date range picker and allows the user to specify a time for each calendar

![timepicker](https://cloud.githubusercontent.com/assets/1387956/4456668/1c28e22c-488d-11e4-9a0c-33f2a212be59.gif)

I think these tests are covered by the tests here: https://github.com/BrandwatchLtd/daterangepicker/blob/master/test/daterangepicker.tests.js#L251